A year ago, Mr Murray was assistant head at Cheam independent preparatory school in Berkshire. "I'm just trying to keep my feet on the ground," said the 53-year-old who resigned this summer from the pound;5,400-a-term school.
Next month, his two children's books, Mokee Joe is Coming and Mokee Joe Recharged, will be printed by publishers Hodder Children's. A third novel will be published next spring. The books tell the story of a 10-year-old boy haunted by an other-worldly creature called Mokee Joe.
Mr Murray's deal with Hodder follows the unexpected success of the first Mokee Joe novel, printed by vanity publishers Pen Press, which sold 12,000 copies by word of mouth.
"I always felt that Mokee Joe was something special," Mr Murray said. "But I didn't expect it to happen so quickly. Spooky material is really in at the moment, so an agent hopes to have a film deal by Christmas. They were mentioning names like Peter Jackson."
This summer, Mr Murray handed in his resignation at Cheam to embark on a national tour, promoting his novels. He admits he is daunted by his self-employed status but is comforted by an unexpected nest egg: "First editions of the Pen Press version are selling for up to pound;200 on E-bay. I have 100 copies under my bed."
Meanwhile, he is working on a fourth novel, featuring a seven-foot Viking ghost. "I'm churning them out. I have writer's diarrhoea. But I think I'll always be remembered for Mokee Joe. It has a ring to it, like Scooby Doo."
Regular contact with pupils helped him develop realistic dialogue. He now hopes to seek inspiration during promotional visits to schools. But after 20 years as a teacher it is difficult to sever himself from his past. "If I hadn't been a teacher, I wouldn't have been able to write in the way I do," he said. "I still think of myself as a teacher. But I'm a teacher who's discovering he's a writer as well."