Black Coffee: A Mystery Play in Three Acts by Agatha Christie..An intriguing story concerning a physicist named Sir Claud Amory who has come up with a formula for an atomic bomb. In the first act, Sir Claud is poisoned (in his coffee, naturally) and Hercule Poirot is called upon to solve the case. He does so after many wonderful twists and turns in true Christie tradition.
Librarian's note #1: 'Black Coffee' was written in 1930; that's fifteen years before the use of two such bombs brought an end to WW2.
Librarian's note #2: this is the first of several plays written by Christie, of which the best known is 'The Mousetrap'. Some of the plays, such as this one, have been novelized by other authors and can be found elsewhere on Goodreads.