While visiting neighbor Tillie Adams' residence, in Cabot Cove, Maine, Jessica Fletcher (Angela Lansbury) and Doctor Seth Hazlitt (William Windom) stumble across her body, Seth pronouncing Tillie deceased of natural causes.
At Tibbles Antiques and Collectables, in the Cabot Cove business district, proprietor Benny Tibbles (Dick O'Neill) argues with Emily Goshen (Barbara Cason) over his price increase of the family broach, which she has pawned in his care, when Benny's son, Kevin Tibbles (Shea Farrell), enters to announce Tillie's passing. Emily has served with domestic care for Tillie, while Benny had handled odd jobs for her.
After a memorial service, attended merely by Jessica, Seth, Emily, Benny, Kevin and a Minister, Sheriff Amos Tupper (Tom Bosley) soon informs Jessica that she has been named in Tillie's will, along with the contents of the residence to go to Benny, the house and property to go to the only surviving relative, Great-niece Liza Adams (Lois Foraker), and Jessica to serve as estate executor.
When Jessica enlists Real Estate Agent Eve Simpson (Julie Adams) to appraise the value of Tillie's estate, Eve discovers very few selling points, if any, and seeks to market the residence on the basis of any historic value, while Emily Goshen, on hand to clean, begins to challenge the will under the notion that she has done more for Tillie than anyone else.
Benny Tibbles quickly learns of his inheritance and summons his brother, Wilton Tibbles (David Clennon), and his Assistant, Lauren Hastings (Katherine Moffat), at the upscale Wilton P. Tibbles Antiques Shoppe, in Boston, to drive up to Cabot Cove, to help Benny to market Tillie's antiques. Wilton, knowing that the products could nab much higher profits in the city rather than around a community as Cabot Cove, lunges at the opportunity to appraise Tillie's possessions from a grade higher than Benny could, while Lauren eagerly lunges toward any opportunity to make a play for Kevin.
Eve Simpson, meanwhile, lunges toward any opportunity to make a sale of the Adams' residence, she baiting British national Alastair Andrews (Brian Bedford), who understands a connection between the Adams' residence and Revolutionary War General Benedict Arnold, a convicted double agent, who reportedly kept a mistress within the Adams' household.
But that night, flower child Liza Adams (Lois Foraker) shows up on Jessica's doorstep to demand her share of her Great Aunt Tillie's estate--in cash.
And the next day, tempers begin to flare around the Adams' estate, as Wilton and Lauren haggle with Benny, when Liza shows up to challenge his right to receive a share of the inheritance, while Emily descends from upstairs cleaning, to embark into the round of debate, subsequently refereed by Jessica.
To add fuel to the fiery commotion, Emily reports that Tillie had told her about the distant relation with Benedict Arnold and a hidden treasure somewhere upon the premises, which should go to Emily...or Benny and Kevin...or Liza...or Wilton and Lauren...or Alastair...or Eve or Jessica...or whoever can find it first.
One morning later, Jessica and Seth return to the Adams' estate, to discover its front door unlocked, and its parlour door open, as they stumble across another body, this one before the hearth, bludgeoned by a fireplace poker, across from the missing embroidered sampler, reading, "Reflect and Pause," as "Benedict Arnold Slipped Here."