You would have been able to see the teenagers around the house as you came down the driveway. The familiar sound of a small town, high school graduation party would have bounced across the property, silhouettes breezing through the glow of the home and spilling into the grass lawn.

It was a mild, clear, mid-September night; summer's final call.

Around 2 a.m., two teenage boys left the party and walked away into the dark. They found an old, unlocked station wagon parked on the neighbouring acreage with the keys inside, got in and drove off.

The driver lost control within minutes. The car crashed into the woods, rolled and hit a tree hard enough to knock the timber down.

The driver died. The passenger was thrown from the car and landed in a mossy ditch. He lay there, unconscious, until the next afternoon.

The site of the crash on Sept. 15, 2012. (CHEK News)

Nearly eight years later, a wooden cross stands at the side of the road to mark the crash site on B.C.'s Salt Spring Island.

The surviving passenger is about to turn 25. A landmark civil lawsuit involving a number of people involved in the party and the crash has been winding its way through the courts for his entire adult life.

The case is finally going to trial in B.C. Supreme Court on Wednesday.

The trial will determine whether the couple that hosted the Saturday-night party is, in any way, legally responsible for what happened to their teenage, underage guests: the death of one and the catastrophic, life-altering injuries of the other.

In doing so, it will answer a question that's gone relatively unanswered in Canadian law: Can adults who have minors drinking on their property be held liable for disaster caused, or suffered, by their underage guests after they've left?

The outcome could change the way adults and parents in B.C. think about teenagers drinking in their homes.

Ryan Plambeck, 18, and Calder McCormick, then 17, were guests at Stephen and Lidia Pearson's home for the party on Sept. 15, 2012. The couple lived off Epron Road, on a plot of acreage in the northern end of Salt Spring Island. They had children around Plambeck and McCormick's age.

The party began as a birthday celebration and morphed into a grad party as word got around.

The Pearsons' neighbours lived on their own acreage across the street. That couple was selling their 1992 Subaru Loyale and had it parked, uninsured, on their property. In honest islander fashion, the owners had left the white station wagon unlocked with the keys inside, in case any curious potential buyers wanted to take it for a test drive.

Whether Plambeck and McCormick knew the car was there, unlocked with the keys inside, is a point of contention.

Plambeck drove away, pulled onto North End Road and headed northwest. McCormick was in the passenger seat. Neither wore a seatbelt.

Ryan Plambeck, 18, pictured in a file photo. (CHEK News)

North End Road is a narrow, twisting road curling around the forested northern tip of the island.

Plambeck lost control on one of the first curves he encountered. The car crashed and rolled into the trees, coming to rest in a ditch shrouded by foliage.

A report from the B.C. Coroners' Service said Plambeck was likely dead on or shortly after impact. McCormick was hurled out the passenger door as it flung open during the rollover.

No one found the wreckage until 4:45 p.m. the next day, when a farmer noticed skid marks on the pavement leading into his property.

Salt Spring Island is home to about 10,000 residents, many of whom work as artisans, farmers, musicians and entrepreneurs. The island is the largest of B.C.'s Southern Gulf Islands, which lie between Vancouver Island and the mainland. (Nicole Mordant/REUTERS)

Court documents said McCormick had severe, traumatic brain injury and a long list of other ailments. He was airlifted to Victoria General Hospital in critical condition. As the news filtered out, a hush fell over the island.

"In a small town, nobody finds out about it the following Monday," said Rob Pingle, who was the Salt Spring school trustee at the time of the crash. "Everyone in town knew on Sunday that something terrible had happened."

Salt Spring Island is the largest of B.C.'s five Southern Gulf Islands, clustered together between Vancouver Island and the mainland.

Locals are known for putting lifestyle first. With its mild climate and laid-back feel, it's a place people go to enjoy life as they like and appreciate two degrees of separation between neighbours, instead of six.

The car Ryan Plambeck and Calder McCormick used to leave the party on Sept. 15, 2012, pictured after the crash. The 1992 Subaru Loyale was up for sale and uninsured. (CHEK News)

At the time of the crash, Pingle said, locals weren't concerned about how it happened, or who might have been at fault.

The fallout from the crash began in 2014, when McCormick filed a lawsuit against the Pearsons claiming damages for his permanent injuries.

"He is essentially walking wounded, as a brain-injured person young man. He'll never be competitively employable," said McCormick's Vancouver-based lawyer, Michael Wilhelmson.

The lawsuit alleges the Pearsons, as hosts, breached a duty of care they owed their teenage guest by letting him drink underage on their property. The suit also claims the adults should have stopped McCormick from leaving in a drunken state — especially, it alleges, when they knew there was an unlocked car ripe for the taking next door.

"Basically, [they] did nothing to stop him from ending up on the road," Willhelmson said, referring to the notice of claim.

None of McCormick's allegations has been proven in court.

The coroner's report found Plambeck was impaired by alcohol and cannabis at the time of the crash. Toxicology studies found his blood alcohol level was higher than the legal limit for drivers.

The report, released to CBC News, also said Plambeck did not have a valid driver's licence as his learner's had expired.

Homeowners deny allegations

In their responses to the civil claim, the Pearsons unequivocally deny the allegations. They claim McCormick or his own parents were responsible for the teen's wellbeing. They also point to an alleged pattern of poor behaviour.

The Pearsons claim McCormick had a history of drinking and using marijuana, and that his parents should have done more to ensure their son made it home safely — particularly after their second son returned home from the same party without his sibling.

Unlike licensed businesses like bars and restaurants, which have a clear statutory duty not to overserve customers and to ensure they have a safe ride home, "social hosts" serving alcohol at home don't owe a special duty of care to anybody injured by a guest who drank alcohol at their event.

The crash site on North End Road, near the northern tip of Salt Spring Island. (CBC)

Social host liability

When it comes to minors, social host liability is still a relatively novel issue in Canadian law.

A 2006 Supreme Court of Canada ruling is considered to be the leading reference on the issue. In that case, the top court found two adult hosts were not responsible after their adult guest drunkenly drove away from the party and crashed into another vehicle.

But the case didn't touch on the different responsibility dynamics between parents who host teenage partygoers. The case also generally left open the possibility that hosts could be held liable in some circumstances, if they are directly implicated in creating a major risk of an accident.

At trial, McCormick's lawyer will try to convince the judge that's what the Pearsons did in 2012.

If the judge finds the couple legally liable for McCormick's injuries, it would set a trial judgment precedent for adults who have teenagers drinking in their homes.

"It would be quite dramatic ... It could have a bit of a chilling effect on how people socialize in British Columbia," said Dan Coles, a Vancouver-based lawyer specializing in liquor law. (Editor's note: Dan Coles has previously represented CBC in legal proceedings concerning media law, unrelated to liquor law.)

McCormick is also suing Plambeck in the same claim. He alleges Plambeck put his life in danger by inviting him into the car in the first place. He claims Plambeck was drunk, high, speeding and texting behind the wheel.

"There's no surprise that the court's going to be looking to Plambeck — he was the driver of the vehicle, there's no question ... The court will need to assess what his share of the blame is," Wilhelmson said.

"It's regrettable that we've come to this point ... but, unfortunately, these things happen. And, yes, there's a lot of feelings about this case. It's a small community. People know other people."

A lawyer has denied McCormick's claims on behalf of Plambeck.

The trial is expected to last around a month.