Q.E.D.

A wealthy, if abrasive, Harvard professor quits in the middle of a lecture and moves to London where he uses his scientific background to investigate a missing person from a yacht off the British Coast.

Deverill is alerted to a cross-country automobile race for which he lends his talents to one of the entrants. Kilkiss also assists one of the foreign entrants.

Deverill is contracted to develop a safer detonation mechanism for mining. Meanwhile Jenny and Phipps are kidnapped at a soup kitchen as a way to pressure Deverill into using his invention for political purposes.

After discovering a potent nerve agent, an associate of someone with whom Deverill has been working is shot on Deverill's doorstep. With his dying breath, the man gives Deverill a clue about a train to Zurich.

Jenny visits her sick aunt, from whom she learns of a potential ghost haunting the residence. She then enlists Deverill to come investigate.