Arrgh. What was I thinking? When Netflix's algorithm predicts I'll find a movie to be mediocre, I should probably just believe Netflix. But it looked so good! Robert Mitchum! Jean Simmons! Film noir! But no.
Mitchum plays Frank Jessup, a Beverly Hills ambulance driver with dreams of setting up an automotive shop specializing in sports cars. He's got a steady girl, Mary. He's struggling, but on the right path.
Oops! His ambulance is called out to a mansion up in the hills, where fantastically wealthy Catherine Tremayne has nearly suffocated in her bedroom, due to a gas jet somehow being turned on. She's OK, but the call gives Frank the unfortunate chance to meet the beautiful stepdaughter, Diane (that's Jean Simmons). She loves her daddy, a washed-up Brit novelist, but clearly hates Catherine. Did she try to do Catherine in? Yeah, probably.
It would just be a chance encounter, except that Diane stalks Frank back to the station, and corners him in his after-shift hangout. Before you know it, Diane has easily driven a wedge between Frank and Mary, enticed Frank into accepting a job as a driver for the Tremayne family, and displayed all sorts of devious, deceptive, and dangerous behavior.
It's all fun and games until someone drives their car off a handy cliff, though. Things go downhill (ha!) from there, with a far-fetched courtroom strategy, and far too much dialog. Mitchum just kind of goes along with everything, to his ultimate disappointment.