David Budd: you had one job, mate. After apparently failing to protect his secret lover Julia Montague – a hawkish home secretary with her eyes on No 10 – the anxious Scottish protection officer is trapped in a conspiracy hall-of-mirrors where nothing is what it seems. As the extended finale of Jed Mercurio’s political nailbiter looms, here are the key questions that need to be answered.

1. Who was really behind the attack that took out Julia?

She survived a sniper ambush but apparently not a bombing. Was Julia’s murder just the latest escalation in the terror campaign putting the whole country on edge? Or was it part of a scheme hatched closer to home? Weaselly special advisor Rob recently admitted to police that he had plotted against Julia with counter-terrorism minister Mike Travis and chief whip Roger Penhaligon (her sniffy ex-husband), but insisted the intention was only to embarrass her politically. Since the bomb was apparently triggered by a pressure sensor on stage, it relied on poor new PR advisor Tahir Mahmood being ordered to interrupt Julia mid-speech. How would the real bombers have known about this intervention unless they were aware of the vengeful politicos plan?

2. Will Julia miraculously return from the dead?

The first rule of TV drama is that if you don’t see the body, a dead character could always come back. Yet Bodyguard has gone to great lengths to insist codename Lavender has been buried for good (albeit it a private, closed-casket funeral). In the show, it was PM John Vosler who confirmed Julia’s death, and surely he would not lie so publicly if the overarching plan was for her to make a “gotcha!” comeback to nab the real culprits. In the real world, Mercurio has done the rounds insisting it was always his intention to kill off Julia to underline that in Bodyguard no one is safe. All it would take is one word to definitely bring her back (although that word is probably “prequel”).

Anne Sampson Photograph: BBC/World Productions/Sophie Mutevelian

3. Are the cops in on it?

When looking for homegrown conspiracies, MI5 is the easy option: hatchet-faced security service director-general Stephen Hunter-Dunn looks as if he has overseen more than his fair share of morally murky black-bag operations. But the Met’s counter-terrorism commander Anne Sampson also seemed constantly at odds with Julia, calling her “dangerous” and recruiting David to spy on his principal while they were stashed in adjoining hotel rooms. Has the Met simply taken some rather extreme measures to protect its jurisdiction?

4. Is Longcross merely MI5’s attack dog?

“Richard Longcross” – either a false name or one carefully scrubbed from intelligence databases – is the MI5-assigned vampire who carefully wipes CCTV wherever he goes. He was the operative who passed the tablet loaded with blackmail-ready kompromat to Julia. He also made an intimidating housecall to David’s nurse wife Vicky. Now, thanks to David’s efforts, he has been implicated as the man who sourced the suicide-bomb vest for the train attack that launched the whole series. We’ve seen him answer gruffly to Hunter-Dunn but he seems to have a lot of operational leeway – could he be the real mastermind, or be working for someone else?

5. What is Charlotte Foxfield’s story?

From our glimpses at the kompromat material – including references to drug abuse and dodgy financial transactions – the name Charlotte Foxfield was apparently connected to a sexual assault. Even before David acquired the tablet, googling Foxfield’s name was seemingly enough to bring Longcross and some MI5 heavies barging in to an internet cafe. Could Charlotte be the key to unlocking the whole sordid case?

6. What’s the deal with snarky Chanel and the crime boss?

Disgruntled employee or hostile asset? Chanel Dyson. Photograph: Sophie Mutevelian/BBC/World Productions/Sophie Mutevelian

Impressively insolent PR advisor Chanel almost ruined one of Julia’s many TV appearances with an “accidental” coffee spill. Then, after she was fired, she tried to flog inside info to the tabloids to discredit the home secretary. Disgruntled employee or hostile asset? Even before Julia’s death, David had clocked Chanel being picked up by an intimidating-looking black Land Rover driven by an intimidating-looking beefcake (later identified as organised-crime boss Luke Aitkens). Another seemingly chance meeting with Chanel saw her chatting up David in a coffee shop while breezing past the fact the server called her “Sam”. Either Chanel/Sam is crucial to the conspiracy or she is an impressively over-it Jed herring.

7. Who is Vicky’s new fella?

David’s fraught home life with his estranged wife Vicky got even more complicated when he discovered she had a new man in her life. So far he has been mentioned but never seen, which suggests he might be a character we’ve already met or at least one tasked with getting close to Vicky. That would provide leverage over David, who still seems devoted to his wife and kids.

8. Why does David think he needs a sniper rifle?

Before he acquired the kompromat at the end of episode five, David had a rainy rendezvous with an ex-soldier turned arms dealer who, it was implied, he had dealt with before. Using a Russian Makarov handgun as collateral, David put in an order for a PSL marksman rifle. Was he trying to trace where his old army comrade Andy got his hardware from, or does he have some of his own sniping in mind?

A plague on both your houses … Romeo and Juliet. Photograph: Everett/REX/Shutterstock

9. Is the whole thing just a really weird spin on Romeo and Juliet?

Of all the conspiracy theories swirling around Bodyguard – many of which hinge on David having some sort of dissociative identity disorder – there is something appealingly romantic about the suggestion that Bodyguard is a funhouse-mirror version of Shakespeare’s greatest tragedy. You have a Montague involved in an illicit love affair, an escalating tussle between two “families” (the Met and the security service) plus David attempting to take his own life when he thinks his lover is dead. It would certainly provide a good tagline for the cliffhanger-addicted series: for there never was a story of more “woah!”.

10. Will there be a second season?

After such a record-smashing launch – and the news that Netflix has picked up Bodyguard rights for the rest of the world – there is no doubt Bodyguard will return in some form. Will David be part of it? First, he’ll have to survive the finale …

Bodyguard’s finale airs 9pm Sunday on BBC One