Murray, Mina, Connor, and Shane come across a strange boat one fine day, stranded on the shore of their town. It resembles a drakkar, a Viking boat, has torn sails and a name on its hull in Greek letters: Metis. On board it shows the traces of a series of mysterious events that led him there, besides a very strange cube where numbers are marked, and a notebook with the following written on the cover: Ulysses Moore - Notes for the thirteenth book...
The four friends decide to set sail, and the boat takes them where they never imagined they would go...