Two lowly office workers Sam (Mathew Baynton) and Phil (James Corden) become caught up in a deadly criminal conspiracy after Sam answers a ringing phone at the scene of a horrific car crash.
After somehow managing a daring escape from their would-be captors, Sam and Phil are now on the run, on the edge and on each other's nerves. It's gonna take a huge leap of faith for Sam and Phil to turn back and face the very people that are threatening them, their loved ones and their town. And as friends and family are dragged into this deadly conspiracy, Sam and Phil's friendship is tested to the limit. They have to expose Reid's evil development plans, save the town, uncover double agents, and rescue their loved ones - all of which means putting themselves right in the line of fire. Can Sam step up and prove himself to be the man that Lizzie wants him to be? Or will Phil's childish antics finally prove their undoing?
Having agreed to take care of the hunted and wounded Marat, Sam and Phil return back to Phil's house where his mum Linda proves surprisingly resourceful. With spies shadowing their every move, our heroes inadvertently bring the dangerous plot right to their doorsteps and ultimately, to the council offices. By arranging to hand over Marat to the care of MI5, they think they can wash their hands of their troubles. Yet the duplicitous Agent Smoke has other plans and just as our two unlikely heroes start to figure out what is afoot, they become high-value fugitives.
The devious Scarlett sends Sam and Phil on a mission to retrieve a music box, which has fallen into the hands of eccentric Russian exile Marat Milankovic. Armed only with the ransom money they found in the back of Walker's car, the duo set off to buy it back. But with the vengeful Lau still seeking payback, Sam and Phil find themselves arriving empty-handed at a drug-fuelled house party. Inadvertently stumbling into the middle of a poisonous assassination plot, the boys are plunged deeper into a world of betrayal, bullets and blood.
When Lau shows up at the council offices, Sam successfully negotiates the safe handover of Scarlett in exchange for Lau's nephew Jason. But Phil has his own ideas and nearly scuppers the plan. Narrowly escaping, they pay a visit to Phil's mum Linda before taking Scarlett back to her husband. But it's not the happy reunion they imagined, and Sam and Phil must go on the run from both cops and criminals, until finding temporary safety in the hands of enigmatic MI5 agent Walker.