Justin Thyme is a self-made billionaire living in a castle overlooking Loch Ness. The day he turns thirteen, he receives an anonymous gift: a fabulous watch with a puzzling message hidden on it. When he tells his father of his plans to build a time machine, the Laird of Thyme reveals tantalising fragments of past espionage and warns his son of a ruthless enemy keeping him under constant surveillance. At first, Justin fails to take Sir Willoughby seriously, but when a stranger arrives claiming to be his long-lost grandfather, Justin is wary especially after his beloved Nanny insists the old man is an impostor.
Justins TV celebrity mother departs on a Congo expedition with her eccentric film crew and Eliza, a computer-literate gorilla. Whilst returning, Lady Henny is abducted, and clues prove that the kidnapper has inside information; someone in Thyme Castle must be a spy or possibly Sir Willoughbys old enemy in disguise. Everyone is under suspicion: Justins nervy tutor; their snooping housekeeper; the theatrical gardener; an ex-royal butler; and Mrs Kof, their freakishly strong cook.
Suddenly, the race against time is on. Can Justin convert his vintage motorbike into a time machine, rescue his mum and discover the identity of their resident spy in less than a week ... or will the dreaded Thyme Curse claim another life?