Dorrie Ambler suspects madcap heiress Minerva Minden wants a "Patsy" for another woman's hit & run crime. They look alike, they act alike and the resemblance is close enough that Mason begins wondering who he's actually representing. Accompanied by private detective Paul Drake, his investigation takes him all across town picking up leads, and coming within arm's reach of a killer.
The look alikes both hire and lie to Mason. The car used was stolen for a getaway. For immunity from prosecution, thief Dunleavey Jasper claims Minden shot Ambler.