Triplets Danya, Darka and Diana come to visit their grandmother. This visit will definitely not be boring, because their grandmother works in an amazing Museum of Mysteries - an old mansion full of secrets, artifacts and traps that once belonged to the famous detective Matthew Faust. The children do not realize that the museum will soon become a crime scene, and the three of them will be caught in a whirlwind of mysterious, exciting and dangerous events. Who committed the crime and what do the nooks and crannies of the Museum of Secrets and the Past hide? Where did the puzzle box go and what role do the British mechanical specialist and the huge black cat Mystery play in all this? Find out together with the triplets and enrich your English at the same time! English!