It's no surprise to Marcello Mousetti when he receives an urgent message from the Prime Minister of England to come to London-immediately. The Great Westminster Clock, known around the world as Big Ben, has mysteriously stopped ticking. Marcello and his friends, Tilly and Taylor, take up the challenge and whiz from Pisa to London through a cyberspace Mouse Operating System called Web-MOS. Upon arrival, they meet an oddly disguised detective investigating the theft of precious jewels from a local museum. But what do stolen jewels have to do with a silent clock? And who's secretly watching their every move? As the story unfolds, Marcello and his friends make a major discovery that takes them into a tangled web of mystery and danger.