Cameron Mitchell is a Sam Spade-Philip Marlowe styled PI whose services are engaged by an old acquaintance (Anderson) to uncover the plot behind a threatening letter. David (Bixby) is employed by Anderson as the gardener on her vast estate, but his attentions are diverted by the randy teenage daughter (Holmes), and the implication that he's behind the extortion plot.
As the other reviewer remarked, the dialogue is reminiscent of the forties film noir, although less refined (the metaphors are simpler than the Paraprosdokian dialogue that was a signature of Bogart and the film noir genre). Veteran character actor Mitchell plays his Spade-Marlowe inspired character with aplomb (an affable, wily old-school operator with all the appropriate motifs) and fellow tough guy Anthony Caruso appears as a Mafia Don with whom Anderson was once well acquainted.
Bixby (and for that matter, the Hulk) are essentially peripheral to the storyline as Mitchell takes centre stage in this Jack Colvin directed episode. There's a good Hulk-out scene where he transforms after being pinned beneath a car when some goons discover Mitchell spying, but otherwise, this is "Chinatown" with a twist of lime and one of the highlights of the series.