Tick is a normal 13-year-old boy until a strange letter changes his life. The first of a series of cryptic messages, the letter explains that his world is in danger. To save his reality, Tick must solve a series of riddles. Luckily, he is not alone and soon makes two friends from other parts of the world, who have been receiving the same clues. Together they race against time to protect their world, realising along the way that theirs is not the only reality at stake.