Mr Flatley is excited when he gets a letter saying that his Great Aunt Jemima has left him a million pounds in her will. Of course, all the students of St. Hope's immediately try to get into Flatley's good books, hoping to get a share of the money. While Flatley is celebrating however he receives a ransom note threatening to blow up the school unless he turns down his share of the money and warning him not to go to the police.
The note is taken to HQ where Frank discovers traces of Dugranite on it, a rare but powerful explosive - finding this, they know that whoever sent the note is serious - there is a bomb in the school and Rose finds a DNA sample on the envelope. They are also alarmed to discover that the last delivery of Dugranite was six weeks ago - to SKUL. Flatley is in a state of panic but Frank assures him he will find the bomb and defuse it. Mrs King does not know about the bomb so is annoyed when Flatley tells her, "Frank is my new best friend". Frank then gives Oscar, Carrie and Rose a task: Flatley's other three relatives will be arriving for the reading of the will in Flatley's office and they are to get a sample of DNA from them to compare with that of the bomber - presumably one of them is the bomber and working for SKUL. The other relatives are Jeannette, a posh vicar who's young people's drop-in centre is in danger of closure due to lack of funding, Nozzy, a failing rock star, and Hamish, a Scottish university Chemistry lecturer. However when they compare all three DNA samples, none of them match the bomber's. They are forced to conclude that this means the bomber is someone else, and they continue searching.
Rose, however, examines the note and notices that to prevent handwriting analysis, the letters have been cut out of an American newspaper. She does some more research and discovers that one of the relatives, Dwayne, is living in America. He has a certain fondness for kittens and blew up his house in an experiment involving Dugranite! He was now renting a lock-up around the corner, where Rose goes to search for more clues. What she does find are lots of kitten photos and a poster reading SKUL, partly covered by more kitten photos. Rose removes the photos and is shocked to discover that Dwayne doesn't work for the Grandmaster, but for a charity - Save Kittens with Unconditional Love. She is also alarmed to discover a small sample of liquid Dugranite - it had been brought into the school in a vase of flowers. She reports this to Frank, who has been forced into the meeting where the will is being read out by Mrs King, who suspects him of trying to get hold of Flatley's money.
Meanwhile Oscar and Carrie find Dwayne in a store cupboard and that he has bugged the meeting. Before the solicitor reads the will, Flatley interrupts much to the annoyance of the solicitor and demands to know which one of his relatives sent him the note about the bomb. It is then revealed that each of the relatives had received a ransom note, threatening Jeannette's church, Nozzy's shed (where he kept his drumkit) and Hamish's lecture theatre. Dwayne listens as the relatives in turn refuse their share of the money, but when Flatley accepts his, he detonates the bomb in despair. When Oscar shouts at him, "You'll blow up this whole school!" he replies sadly, "If SKUL don't get the money, life's not worth livin'." Carrie however tricks him into believing that Flatley kept kittens in the school and that blowing up the school would make Dwayne a kitten killer. He immediately goes to stop the bomb detonation but discovers that he can't. Oscar sends a Morse Code message to Frank by banging on the pipes, and Frank jumps up and throws the vase out of the window, with seconds to spare.
The solicitor then announces that because Jeannette, Nozzy and Hamish refused the money, it automatically went to Flatley. He is delighted by this news but his happiness is short-lived when the solicitor takes the million pounds for himself, saying that it was because he had been worked overtime and had his time wasted, leaving Flatley with five pounds, which the other relatives think is hilarious and fall about laughing. Mrs King, however, is furious at this and snatches the five pounds from Mr Flatley, as he owed her five pounds when she lent him some to buy a sandwich. A devastated Flatley runs out of his office into the corridor where the rest of the students are waiting expectantly, and sobs, "I've spent it all ... on a sandwich!" to which everyone responds by giving a sigh of disappointment.