A few episodes before "Death of a Stone Seahorse", one of the baddies on "Cannon" was Paul Michael Glaser--otherwise known as 'Starsky' from "Starsky and Hutch". Now, with "Death of a Stone Seahorse", David Soul (Hutch) is the killer AND a drug dealer!! How DID these two end up being cops just two years later?! The show begins with an awkward scene. That's because when a guy discovers that Sean has been dealing in drugs, he does what no sane person would ever do--confront the guy in the middle of no where with no witnesses! This is an incredibly dumb scene--it's fortunate that the rest of the show is much better.
As Sean is a dirt-bag, he of course doesn't admit he killed the man but does something really awful--he convinces his nice but rather unstable sister (Sondra Locke) that SHE killed the guy! Given that she's rather fragile emotionally, she isn't sure what happened--and it's up to Cannon to save the day.
In this show, Cannon is a bit more physical than usual and gets to beat the crap out of Sean TWICE! In real life, I would have put my money on Soul, but with TV you do need to occasionally suspend disbelief! Overall, an interesting episode and one that is quite good even if the initial murder was poorly constructed.