And So to Murder

And So to Murder by John Dickson Carr (as Carter Dickson), a Sir Henry Merrivale mystery.
DEATH RIDES THE TUBE...
The speaking-tube whistled. Monica flew at it. "Who are you? What do you want?"
She bent her cheek to the mouth of the tube to listen for an answer. Something was happening inside the tube. She jumped back.
Something which looked like water, but was not water, spurted in a jet from the mouth of the tube. It splashed across the linoleum.
There was a hissing, sizzling noise as half a pint of vitriol began to eat into the surface of the floor.
The footsteps in the room above began to run.
Monica Stanton has written a saucy best-seller that has landed her her dream job, scriptwriting for a movie studio. Things turn sour quickly as she's saddled with a mentor she despises After someone makes a gruesome attempt on her life, however, her feelings begin to change about him as they are forced together during the investigation.
Theories of Nazi "heiling enthusiasts" and espionage soon take form, leading to the entrance of Sir Henry Merrivale, who now works for Britain's Military Intelligence division. Only Sir Henry can wade through the "fat-heads" and schemers to get to the bottom of this amusing and clever mystery.