Boom! tells the story of two best friends, Charlie and Jimbo (a nickname for James). When Jimbo's sister, Becky, says that the teachers are going to send him to a school for mentally ill children, Jimbo and Charlie sneaked into the staff room, where they hid a walkie-talkie to eavesdrop on the teachers' conversation, in order to confirm what Becky said was true. None of the information they hear means anything (which points to the fact that Becky was just trying to scare Jimbo), except for the surprising fact that their teachers both Mr. Kidd and Mrs. Pearce is speaking another language. After a while of dangerous investigating (for instance, sneaking into Mrs. Pearce's attic) they were approached by a man in a suit at a restaurant who told them to leave their teachers alone and then promptly burned a hole through the table they were sitting at with his finger. They disobeyed his order, however, and Charlie was kidnapped and taken to the Sagittarius Dwarf Elliptical Galaxy, where he had to fake happiness or else face certain death. But, Jimbo did not seem to know this. After a while of Jimbo investigating Charlie's "Spudvetch!" notebook (their secret notebook for gathering information) he discovered that his best bet to find him would be on the Isle Of Skye, in Scotland. He and his sister, who he had managed to convince to come with him, eventually arrived there, although with much difficulty, and inside an abandoned shack, a mysterious portal opened. Jimbo got sucked into Sagittarius Dwarf Elliptical Galaxy, but his sister stayed on Earth, unaware. He found Charlie and, with much difficulty, escaped.
After a while Mr. Kidd and Mrs. Pearce were fired from the school as a result of the kidnapping. They went for revenge on Charlie and tried to kill him. Luckily, the FBI already knew what was going on and had been watching them. They shot Mr. Kidd and Mrs. Pearce and then said that if they ever told anyone about Mr. Kidd and Mrs. Pearce, they would be hunted down and killed. They decided they did not want to be killed, so returned to their normal lives.
Gridzbi Spudvetch! was published in 1992 by Walker Books. As mentioned in Boom!, Gridzbi Spudvetch had many faults. Mark Haddon admitted that 'no one could pronounce the title and know what the story was about until they read it', and also mentioned that the book was 'full of references to floppy disks, cassette players and Walkmans'. The book went rapidly out of print.
The book would have stayed out of print, but over the years several people commented about how much they loved the book. Alison Williams, the teacher of Lilac 4 from SS Philip and James Primary School in Oxford, said she had been reading the book to her children and how much they loved it. To prove this she sent letters from the children to Mark Haddon, which were all kind and funny and very complimentary. With some inspiration Mark Haddon made a new edition, which was published in 2009 under the title Boom!. The book is dedicated to them.