Frank Morningside, assistant at The National Press Archives on Fleet Street, is receiving nasty poison pen letters. His superior Toby Lorn wants to put a stop to it, so he calls on his friends Sally and Johnny Heldar.

Married amateur sleuths, the Heldars agree to go undercover, posing as researchers to scout out the many suspects in the Archives. After all, Fleet Street is home to plenty of seedy types. But, soon after they begin, they find a body – bludgeoned to death by a box of glass negatives.

Suddenly, the genteel world of the archives is a tangled web of suspicion. When another murder swiftly follows, the Heldars worry that one of them maybe next . . .