Lily, Robert and Malkin get the chance to spend the Christmas holidays in New York. Almost immediately upon arrival, the friends receive a note from a strange boy who has lost his memory and asks for help. It seems that he is being held captive by his own aunt - a mysterious scientist who is ready to do anything for the sake of her terrible experiments. Trying to unravel the mystery of their new acquaintance's family, Robert and Lily dive to the very bottom of the ocean. But will they be able to find the answers to their questions before it's too late?...The fourth and final book in the Mechanical Heart series is about the exciting adventures of a professor's daughter, a watchmaker's son, and a mechanical fox in the United States at the end of the 19th century. In PDF format The publishing layout of the book is saved in A4.