The famous physicist, Sir Claude Aymory, turns to Hercule Poirot for help, convinced that he is in danger. The little Belgian immediately calls on his longtime friend and partner, Captain Hastings, and they rush to the scientist’s house. But Poirot does not get to meet Aymory—Aymory has been poisoned. And, at the same time, the open formula for a super-powerful explosive that Poirot had discovered has vanished. The circumstances of the crime are such that it must have been committed in a closed room—yet no one among those present had left the house. That means the murderer is still here…