So Many Steps to Death book by Agatha Christie

So Many Steps to Death by Agatha Christie. Original British Title: Destination Unknown. Characters include Thomas (Tom) Betterton, Hilary Craven, and Leblanc. From inside the front cover: Scientists were disappearing at an alarming rate...Then Tom Betterton, a brilliant nuclear physicist, vanished. But Scotland Yard, the F.B.I. and the Secret Services of other countries still could not discover the pattern. Betterton's wife possibly knew more than she was telling, but except for a last strange warning, she couldn't tell any more...she'd died after a plane crash in Casablanca. So another woman agreed to impersonate the dead woman. As Mrs. Thomas Betterton, she could lead government agents to her missing "husband." The improbable masquerade led her deeper and deeper into the African wastelands and closer and closer to the center of the plot-and to death! From the back cover: Lovely red headed Hilary Craven wanted to die. The sleeping pills were ready on her bedside table, when a knock so