Stamp collector, Harry Fentress has gone missing, and the police want to know the truth from the last person who saw him, his friend, Nils Murchison. He arrived from Boston last week to visit, but then several days ago he vanished, disappeared, simply evaporated from Nils Murchison's penthouse forty floors up. Where is he, and what happened to him? Does the mysterious stamp collection left to Nils by his Uncle leave any clues?