Eddie and Paul, two Americans on parole, find themselves working under the strict supervision of Louie at a bustling diner. Paul, who possesses a quirky personality reminiscent of a spoiled child, dreams of becoming a filmmaker, while Eddie prefers to immerse himself in the world of comic books. Throughout the film, brief glimpses of Eddie's comic book readings hint at his imaginative escapism, notably excluding a character known as the Blue Iguana.
Their lives take an unexpected turn when Katherine, a charming English lawyer, walks into their lives with a lucrative offer. She proposes $20,000 each for their help with a job in London, obviously aware of their abilities. However, the duo negotiations for $30,000 each, with a firm resolve to avoid causing anyone harm. Reluctantly, Katherine agrees. To facilitate their exit from Louie's grasp, she cunningly uses her knowledge of Louie's conversations against him to convince him she can bring trouble to his doorstep.
The three embark on a journey to London, bending laws along the way, which comes to light when Katherine utilizes this against them. Upon their arrival, they are introduced to Tommy, Katherine's cousin, and Cornelius, who amusingly claims he was once auditioned for a Hobbit role but was overlooked for being too tall.
Their mission is to execute a seemingly straightforward theft from a museum—retrieving what they believe to be just a "rucksack." Yet, the situation escalates when a character resembling Ken Jennings interferes, causing the coveted blue bag to vanish. Complications arise with a menacing character named Deacon, a pub owner often mocked for his hairstyle, drawing the nickname "Billy Ray Cyrus" from those around him. As events unfold, Deacon and his band of clueless followers seize control of a restaurant, leading to an encounter where they execute a successful getaway with the blue bag in question.
The intrigue deepens with Arkady, a somewhat sinister businessman, who is in cahoots with Deacon. He expects Katherine to procure the contents of the blue bag to settle a significant debt. As Katherine recognizes the danger to Eddie and Paul from Arkady's intentions, she refuses to comply, thereby accruing yet another substantial debt.
With their predicament worsening, Eddie and Paul contemplate backing out, but Katherine highlights the peril of potential imprisonment if they choose to abandon the mission. The group, consisting of Eddie, Paul, Katherine, and Tommy, sets up surveillance against Deacon's crew from a vacant building adorned with striking street art.
The plot thickens when Katherine learns that Arkady is seeking a valuable diamond known as the Blue Iguana, a gem with a romantic history involving a Turkish prince and a neglected fiancée who lost it in a game of chance. The heroes devise numerous elaborate schemes to reclaim the diamond and return it to its rightful owner. In one humorous twist, they are barred from a hotel due to a zombie film being shot on location. However, an explosion that occurs unintentionally results in them appearing bloodied, allowing them to slip through the doors disguised as cast members.
In an unexpected turn of events, Paul successfully captivates Dawn, a savvy bartender, by deceitfully claiming to work for NASA, igniting a budding romance. As the chaos unfolds, the stakes grow higher, leading to an atmosphere saturated with violent confrontations and even fatalities. Katherine, holding leverage against Arkady, is ready to play her cards strategically as the group navigates through the tangled web of deception and danger.
