The Isle of Masks (Ulysses Moore #4)

Jason, Julia, and Rick are convinced that Kilmore Cove's long-lost inventor, Peter Dedalus, isn't lost in the present day. He's lost behind one of the Doors to Time, and it's up to the kids to find him! One riddle after another leads them to 18th century Venice, where Peter Dedalus's eccentric inventions are scattered around the city. The kids are convinced that each step brings them closer and closer to the discovery of a lifetime. But Oblivia Newton is hot on their trail, and, from what they can tell, Dedalus is nowhere to be found.