This is the seventh book about the detective Filo Vance, in which, as always, he skillfully investigates an unusual case. One of the guests gathered in a comfortable estate for the weekend dives into the pool and does not leave it in front of several people. Neither the search for divers or the descent of water yields results: a person disappears without a trace. And, although many are interested in the death of the unfortunate, the suspicion seriously falls on the dragon.