This time around, Jessica Fletcher (Angela Lansbury) plans to set her next Murder Mystery in the Blue Ridge horse-breeding country, and so she visits her dear old friend Matt Cleveland (Mickey Rooney), a jokey-turned-trainer at Hampton Farms, in Glen Falls, Virginia.
During her greeting with old friend Wally Hampton (Don Murray), who owns Hampton Farms, Jessica says that she hasn't seen old friend Catherine Noble (Tippi Hedren) yet. Catherine owns the neighboring Noble Farms, which is on the verge of bankruptcy, unless Noble Farms and Hampton Farms' joint star race-horse, Swift Prince, manages a win in Saturday's upcoming Raleigh Handicap event.
A widowed Catherine Noble has an only child, materialistic, pretentious Tracey Noble (Ami Dolenz), who continuously plans her upcoming wedding to fiancé Paul Hampton (Sean O'Bryan), the only child of the widowed Wally Hampton, an otherwise responsible son who enters a banking position, against his father's better judgment.
A widowed Matt Cleveland also has an only child, daughter Jill Cleveland (Shawnee Smith), who follows in her father's business as very capable jockey to Swift Prince, in partnership with Hampton Farms and Noble Farms, sort of like the arrangement between Tracey and Paul, although Jill and Paul seem to share an eye for each other, as well.
Usuallly on "MSW," a widowed mother would have the only son, who becomes "the man of the house," while the widowed father would have the only daughter, of whom is behaves overly protectively, but everyone's banking on a win at Raleigh Handicap by Swift Prince this Saturday...or at least until Matt is struck down in the stable one evening and Swift Prince is injected by a performance-enhancing substance into his "Bloodlines."
Jessica and Jill see to it that Matt is all right once Jessica discovers the "needle in the haystack," by immediately retrieving a syringe cleared of fingerprints in a bed of straw over the ledge of a corner in the darkened stable.
But tempers begin to flare by the manipulative Lloyd Mentone (Stephen Macht), who crusades against a Swift Prince win any which way he can, and bribes Hampton Farms Assistant Trainer Gus Tardio (Don Swayze) into action, as Lloyd fights Paul Hampton at the bank in the processing of Catherine's loan.
Doctor Garney (Frank Farmer) gives Swift Prince a clean bill of health on the day after the attack, he saying that the injection ought to wear off by Saturday, as well as his hoof injury, while Sheriff Clyde Benson (Blake Gibbons) and the others ponder the reason for the perpetrator's scheme and the method behind the madness.
That evening, Jessica works in Matt's office, with no one else around Glen Falls. Catherine attends a meeting with Wally, and Jill accompanies Paul for dinner, as Tracey arrives to invite Jessica to a nearby French restaurant.
But along the rural route, not far from the stables, Jessica and Tracey discover a body, which, as it turns out, has been bludgeoned with a flashlight.
Sheriff Clyde Benson enlists Jessica's capable assistance in investigating the murder, as she discovers that someone has cleverly switched Swift Prince with Victor Way and sent the genuine Thoroughbred off to South America, and now she suddenly realizes that someone will immediately inject a fatal dosage into the substitute horse's "Bloodlines."
The cast is rounded out by Dave Powledge as Delivery Driver, Scott N. Stevens as Deputy Vernon Kelly, and Craig Shoemaker as Scott the Trainer's Helper.
This episode marks the second of two "MSW" appearances each for Blake Gibbons, Craig Shoemaker and Don Swayze, the second of three for Sean O'Bryan, and the fourth of five "MSW's" for Stephen Macht.
(Extra points for Mickey Rooney, Tippi Hedren, Don Murray, and for Sean O'Bryan's big scene with Ami Dolenz, and, of course, for introducing into the series a flashlight as the murder weapon.)