“Nobby” Butcher has been separated from his brother Sebastian for 28 years. During the years of separation, Nobby has become an alcoholic and has started his own life with his wife Dawn and 11 children in the English seaport town of Grimsby.
Sebastian (now Sebastian Graves) has become one of MI6’s top agents. After completing an interrogation, Sebastian comes into information regarding philanthropist Rhonda George, who is hosting a benefit called WorldCure and is a potential target for assassination, and is assigned to go. Nobby’s pub friends also find out that his brother will be at WorldCure and convince Nobby to go and reconnect with him. Sebastian goes to the event and sees a hitman, later known as Pavel Lukashenko, who plans to assassinate Rhonda with a gun disguised as a video camera. As Sebastian prepares to shoot the camera, Nobby sees him and gives him a hug, accidentally causing him to shoot a Jewish-Palestinian boy with AIDS named Schlomo. The spray of blood lands in Daniel Radcliffe’s mouth, giving him AIDS.
The brothers go on the run from the authorities and other assassins, with Sebastian breaking his ankle in the process. Despite Sebastian’s protests, Nobby convinces him it would be best to hide at his home in Grimsby. Meanwhile, MI6 believes that Sebastian has gone rogue. The MI6 send orders to an assassin named Chilcott to track Sebastian down. However, Sebastian calls his handler Jodie and proclaims his innocence.
Chilcott and his men find the two brothers at a pub. Sebastian and Nobby spot them and run away with help from the pub clientele, but Sebastian is hit with two Lonomia poison darts in the process. Nobby is forced to first suck the poison out of his brother’s shoulder and then his testicles to save him.
The brothers travel to South Africa, after Jodie informs Sebastian that Lukashenko was doing a deal with Joris Smit in Tshukaru Bush Lodge. Sebastian accidentally injects himself with heroin, mistaking it for the bone strengthening treatment for his broken ankle. Nobby must assume his identity and go undercover.