The first episode of season two of Serial, the popular podcast from creator Sarah Koenig, went up on Thursday — and it's all about Sgt. Bowe Bergdahl. Bergdahl is a US Army soldier who, one night in 2009, snuck away from his post in Afghanistan and disappeared mysteriously. He was captured by the Taliban and held until last year; he's currently in US custody and facing charges of desertion and endangering the soldiers sent to find him.

Knowing Serial, this coming season will surely be full of interesting revelations about the circumstances surrounding Bergdahl's disappearance. But there's already a lot of backstory, as well as some really important political context.

So here's a guide to what we know about the Bergdahl case, both for people looking to keep up with Serial and people who are just plain interested in an incident that became a major controversy in American politics.

1) What are the basics of the Bowe Bergdahl case?

On the night of June 30, 2009, then-Private Bowe Bergdahl vanished. He left no indication of where he went; no one in his unit could find him the next morning. Apparently Bergdahl's unit was chronically lax about security, so it wasn't hard for him to sneak out.

"The platoon's life became a living hell for the next six weeks as they searched for Bergdahl in the Afghan desert in July and August," NPR's Wade Goodwyn reports.

But the searches were fruitless, as shortly after disappearing Bergdahl was captured by the Taliban. The official story from the US government was that Bergdahl disappeared on patrol, and the true story wasn't known until some time after his disappearance. It's still not 100 percent clear why Bergdahl left, but recently revealed evidence suggests he was running to another US base to expose alleged incompetence inside his own unit.

In May 2014, President Obama announced that he had secured Bergdahl's release. The Taliban agreed to give up Bergdahl in exchange for the release of five Taliban-linked prisoners. The deal prompted a massive political firestorm: Republicans accused President Obama of illegally releasing five dangerous prisoners, thus endangering US national security, in exchange for a traitor. The controversy over the prisoner swap still rages today.

In March 2015, military prosecutors filed formal charges against the 28-year-old Bergdahl. A military judge is currently deciding whether to allow those charges to go to actual trial; a decision is expected in the near future. If convicted, Bergdahl faces the possibility of life in prison.

2) What is Serial going to investigate about Bergdahl?

This season of Serial is structured in part around previously unaired tapes of interviews between Bergdahl and acclaimed screenwriter Mark Boal. However, Serial's producers claim to have no profound revelations about the basic questions surrounding Bergdahl's case, such as his guilt or innocence.

"We’re not holding back on something that the world needs to know," Julie Snyder, an executive producer, said in an interview with the New York Times.

In the same Times piece, Serial creator Sarah Koenig said the show will focus on some broader unanswered questions surrounding the case: "Exactly how long did the search [for Bergdahl] last? What were the consequences of the search? Was this all a search in the name of Bowe? Was this top cover for stuff that they wanted to be doing, but they already knew Bowe was in Pakistan anyway?"

"All of that is super interesting, and we definitely are heading down that path," Koenig added.

This is a new approach for the podcast. Last year, the investigation focused on the guilt or innocence of Adnan Syed, a young man who was convicted for the 1999 murder of his ex-girlfriend Hae Min Lee. The Bergdahl season appears a bit more complicated than a basic whodunit, as New Yorker contributor Sarah Larson writes:

The basic facts in the case of Bergdahl are known, and most parties involved agree on what they are. But what those facts mean, what Bergdahl actually experienced in the Army, his motivations for leaving his platoon, and the many terrible consequences of that decision are more complex, even existential.

In other words: The facts of the Bergdahl case are less the central issue in this year's Serial and more the background necessary to fully understand what Koenig and company are exploring.

3) Did Bowe Bergdahl desert?

At this point, basically everyone agrees that Bowe Bergdahl walked away from his post. It's possible he planned to come back; it's also possible that he was planning on leaving the Army for good (that is, deserting). Hence why the Army brought desertion charges against him.

A classified military report reportedly found that Bergdahl had a habit of taking unscheduled walkabouts. According to the New York Times, he sometimes left his training base "to see a sunrise or sunset." Internal Taliban communications suggest that they captured Bergdahl about a day after his disappearance, so it's possible he was captured during what he planned to be a short expedition.

On the other hand, there's also evidence that he planned to desert. According to the late Michael Hastings's fabulous 2012 Rolling Stone feature on Bergdahl, the young Bergdahl came into the war thinking of it as something like a grand adventure. That didn't survive contact with reality.

"I am sorry for everything," he wrote in an email to his parents just before he disappeared. "There are a few more boxes [of my stuff] coming to you guys." That sure reads a lot like someone saying his last words before his plan to disappear into the Afghan wilderness.

Maj. Gen. Kenneth Dahl, the lead investigator on Bergdahl's case, takes a somewhat in-between view. "According to lead investigator Dahl, [Bergdahl's walkoff] was because he'd come to believe his platoon was in danger owing to lousy leadership," NPR's Goodwyn reported after attending a preliminary hearing in San Antonio this September.

Dahl believes that Bergdahl had a plan to blow the whistle on (apparently largely imagined) "officer incompetence" in his unit: He would run across 20 miles of hostile territory to get to a forward operating base (FOB) called Sharana and inform the general there about what was going on.

Bergdahl's own statements aired in the new season of Serial support Dahl's account, and also suggest he had hoped to uncover new intel about the Taliban and bring it to his superiors. "When I got back to the FOB, you know, they could say, ‘You left your position," he says. "But I could say: ‘Well, I also got this information. So what are you going to do?’"

4) Is Bowe Bergdahl a traitor?

Some people have accused Bergdahl of something worse than desertion. They allege that he actually intended to switch over the Taliban's side. The evidence here is extremely thin — and indeed, military prosecutors have not brought charges of treason or anything like it.

It's true that Bergdahl wasn't thrilled with the United States; his last note to his parents said that "the horror that is America is disgusting." And Sgt. Evan Buetow, Bergdahl's unit leader, claims to have heard "radio chatter" from the Taliban that an American was seeking them out. Afterward, according to Buetow, "all the attacks [by the Taliban] were far more directed." The implication is that Bergdahl provided intelligence to the Taliban.

But it's a big leap from having negative views of the United States to fighting for the Taliban, especially for an American soldier. Moreover, most of what we know about Bergdahl's time with the Taliban suggests he wasn't there by choice. Bergdahl describes himself as a prisoner in publicly released videos during his time in Taliban custody. According to NPR's Goodwyn, he "attempted to escape that very first day and then never stopped trying":

He once succeeded for nine days before running out of food and water and being recaptured on top of a mountain, according to the investigation. For years, Bergdahl was chained in squatting positions or restrained spread-eagle by shackles as punishment for his unending resistance. The Army testified he is no longer fit for duty, his spine and legs are permanently damaged. Bergdahl has said he made 12 escape attempts, a claim the Army does not dispute.

Indeed, US defense officials told NBC last year that Bergdahl was "tortured" and "locked in a small cage."

It's possible both narratives have elements of truth to them. Bergdahl may have provided intelligence to the Taliban but done so under duress. Whatever happened during Bergdahl's captivity, military prosecutors appear to have insufficient evidence to bring any treason charges.

5) Did Bowe Bergdahl get Americans killed?

In a three-week period roughly two months after Bergdahl disappeared, six soldiers from Bergdahl's battalion died. Some critics allege that the soldiers — Morris Walker, Clayton Bowen, Kurt Curtiss, Daryn Andrews, Matthew Martinek, and Michael Murphrey — died looking for Bergdahl. The Pentagon has no evidence to support these allegations, but military prosecutors are bringing up Bergdahl on a somewhat related charge of endangering US troops.

Nathan Bradley Bethea, a former battalion mate of Bergdahl's, was the first to make the charge. According to Bethea, these soldiers all died on missions that were part of the hunt for Bergdahl. Other soldiers in the battalion find his account plausible. Bethea also suggests two other soldiers, Aaron Fairbairn and Justin Casillas, died in an ambush that wouldn't have happened if airplanes hadn't been diverted to the hunt for Bergdahl.

The legal charges against Bergdahl, however, do not depend on him directly getting anyone killed

At the same time, US combat deaths were increasing across Afghanistan as the 2009 troop surge intensified. The Pentagon says there were actually more surveillance aircraft in the area at the time because of the search for Bergdahl. A Reuters report concluded that the deaths happened on missions related to the Afghan election, and after "the period of intensive ground searches had already ended."

Indeed, Defense Department officials have said there is no evidence that any US soldiers were killed because of Bergdahl's actions.

The legal charges against Bergdahl, however, do not depend on him directly getting anyone killed. He's being brought up on charges of "misbehavior before the enemy," which the Associated Press reports have almost never been used since World War II. On these charges, prosecutors are "able to say that what he did had a particular impact or put particular people at risk," Lawrence Morris, a retired officer who has been both the Army's top prosecutor and top public defender, told the AP.

You can, of course, "put people at risk" without actually getting them killed. Indeed, the military's case appears to be that Bergdahl subjected the soldiers sent out to look for him to unnecessary danger.

6) What's the status of Bowe Bergdahl's legal case today?

Bergdahl is not actually on trial yet. "Bergdahl is awaiting a ruling on whether his case will go before a court-martial," the New York Times reports. "Gen. Robert B. Abrams is expected to decide soon what charges he should face."

So the Serial season is debuting at a pretty important time for the soldier.

If Bergdahl's case actually does go to trial on the charges the prosecutors brought in March, he'll face serious jail time: "Misconduct before the enemy" carries a maximum sentence of life in prison. Desertion has a five-year maximum sentence.

However, it's not clear if he'll actually face any jail time even if he goes to trial. Dahl, the Army investigator, said in the September pre-hearing that it would be inappropriate to imprison Bergdahl given the specifics of his case. The attorney presiding over the hearing, Lt. Colonel Mark Visger, reportedly agrees.

"Visger recommended that the charges be referred to a special court-martial and that Sergeant Bergdahl receive neither jail time nor a punitive discharge," Bergdahl's attorney Eugene Fidell said in a statement reported by the Times.

7) Do the Taliban members released in exchange for Bergdahl's freedom pose a threat to the US?

Not as of right now, as they're currently in Qatar under government surveillance. And none of them has demonstrated links to groups planning attacks on the US homeland, though that could change.

Here's a short set of bios of the so-called "Taliban Five" — you can find a very detailed history from Kate Clark at the Afghanistan Analysts Network here.

Mullah Mohammad Fazl: A famous Taliban leader and former chief of armed forces for the group. There's evidence that he's directly responsible for mass murder of unarmed Afghan civilians in both 1999 and 2001 Taliban offensives.

A famous Taliban leader and former chief of armed forces for the group. There's evidence that he's directly responsible for mass murder of unarmed Afghan civilians in both 1999 and 2001 Taliban offensives. Mullah Norullah Noori: A fairly high-level Taliban operative, he led the organization's northern governance zone and was the governor of Balkh province.

A fairly high-level Taliban operative, he led the organization's northern governance zone and was the governor of Balkh province. Khair Ulla Said Wali Khairkhwa: Former Taliban minister of the interior. He's the most senior Taliban member on this list, but according to Clark, he was known as a relative moderate inside the militant group. Allegedly linked to the opium trade.

Former Taliban minister of the interior. He's the most senior Taliban member on this list, but according to Clark, he was known as a relative moderate inside the militant group. Allegedly linked to the opium trade. Abdul Haq Wasiq: Former deputy chief of the Taliban's intelligence apparatus.

Former deputy chief of the Taliban's intelligence apparatus. Mohammad Nabi Omari: A comparatively minor Taliban official from Khost province, but he's actually more important to the Haqqani Network — a militant group affiliated with the Taliban that has its own command structure.

None of these men has well-demonstrated links to al-Qaeda or any other group that targets the US homeland. Some internal Guantanamo assessments allege such connections, but according to Clark, "Many of the allegations are unsubstantiated and bizarre, showing a poor knowledge of the Taliban and Afghanistan before 2001."

The initial deal to free Bergdahl mandated that they stay in Qatar until May 31, 2015. However, the deal — called a "memorandum of understanding" — has been indefinitely extended, and they have yet to be returned to Afghanistan. A December report from the House Armed Services Committee suggests that Qatar would like to send them back to Afghanistan, but there has been no diplomatic progress on sending them home in a way that both parties believe is sufficiently safe.

The most likely scenario for them threatening Americans is if they somehow break that deal, evading US/Qatari intelligence monitoring and returning to the battlefield. The committee report raises questions about the quality of the monitoring, arraying testimony suggesting that the US intelligence community is not taking sufficient responsibility for tracking them.

8) Do the released Taliban members pose a threat to Afghanistan?

Definitely, if they ever make back from Qatar.

According to Anand Gopal, an expert on the Taliban at the New America Foundation, "of the five released Taliban, only 2 have the potential to make an appreciable impact on the battlefield: Fazl & Noori...Khairkhwa isn't a military commander, and the other two are mid-level."

Presumably, that means Fazl and Noori could help the Taliban commit attacks on the Afghan National Army and civilians. The key question about Fazl and Noori going forward, then, is how they'd integrate with the modern Taliban. Both of them were detained in 2001, so they haven't had an organizational role in the Taliban in well over a decade. Will they be able to mesh well with the way the organization is structured today?

It's hard to say. The Taliban is a loose, shifting network of militant groups, and a lot has changed since Fazl and Noori's detention. But there's definitely a risk that their return would help the Taliban hurt Afghans.

9) Republicans say the deal to bring home Bergdahl was illegal. Are they right? And if they didn't like this deal, did they just want to let him rot?

Section 1035(d) of the 2014 National Defense Authorization Act (NDAA) requires that the secretary of defense "notify the appropriate committees of Congress" that he or she has decided to release or transfer an inmate at Guantanamo Bay "not later than 30 days before the transfer or release of the individual."

The House Armed Services report, authored by Republicans, that looked into the legality of the transfer concluded that then–Secretary of Defense Chuck Hagel "made a willful decision to undertake the transfer without providing the 30-days’ notification required" and thus that "the transfer of the Taliban Five violated several laws, including the National Defense Authorization Act for Fiscal Year 2014."

However, it's much more complicated than that. The Obama administration argues that Congress didn't intend for the law to cover a prisoner exchange, which is what occurred in the Bergdahl case. The Obama administration's claim is "not a ridiculous argument, but it's weak," the University of Chicago's Eric Posner told me last year.

Arguably, there's a stronger claim that what the Obama administration did was legal and what Congress did was illegal. Congress regulating prisoner exchanges violates Article II of the Constitution, which gives the president exclusive "commander in chief" powers during wartime. "It's actually quite a hard legal issue, with few real precedents," according to Harvard Law's Jack Goldsmith.

Indeed, constitutional experts generally say there's no obvious right answer to this question. And they all agree that the Supreme Court will never hear the case: No one will have standing to challenge the deal to release the Taliban Five in exchange for Bergdahl, because no single person can show he or she was individually harmed by it.

Despite their qualms about the legality of Bergdahl's release, Republicans have never said Bergdahl should have stayed in a Taliban prison. The GOP critique centers on the idea that the price for his release was too high, not that Obama was wrong to make some kind of deal for him. They also argue that he should stand trial as a deserter if the evidence supports it.

The best articulation of the conservative position comes from Peter Feaver, a former Bush administration foreign policy official and current Duke University professor. "In terms of prisoners released, Obama gave the Taliban the maximum he could of their original demand (they asked for a sixth prisoner, but he died in the interval)," Feaver writes. "The Taliban clearly think they got a very good deal."

According to Hillary Clinton's memoir, the Taliban had been demanding Guantanamo prisoner releases for at least three and a half years before the deal happened. So it's pretty plausible to say the Taliban got what it wanted, and that the damage done to America's efforts to stabilize Afghanistan and weaken Islamic extremists there outweigh the benefit of securing Bergdahl's release.

That's the core point of contention between the White House and congressional Republicans — a controversy that, despite the deal being made a year and a half ago, remains live today.