The grand prize of the 20th Annual Golden State Rally in Monterey is an antique car collection willed by a late millionaire. Mischief develops into mishaps and worse, until an entrant is killed.

A temperamental tennis champion is suspected of murdering a newspaper magnate who had him suspended.

A WWII intelligence colleague, long since thought to be dead, turns up and is murdered.

Mildred is accosted while serving on a sequestered jury, then another juror is murdered in his locked room.

Mac heads south to a police convention on a train filled with officers, Mildred, and the author of Cops and Other Crooks, who is murdered en route.

It seems that Mac's sister is engaged to a con man out to diddle a mining company.