Arden of Faversham has had some excellent news. Through his ruthless business dealings he has come into possession of a huge amount of land once owned by the local Abbey. However in spite of his great wealth Arden isn't happy. He has learned that his wife Alice is having an affair with a lowly steward, Mosby. What Arden doesn't know is that the lovers have made a pact to murder him.
Using Mosby's sister Susan as bait, the murderous pair involve Arden's servant Michael, as well as a local painter and amateur chemist by the name of Clarke. Clarke provides Alice and Mosby with a potent poison to administer to Arden. However the poisoning fails when Arden tastes something strange in his porridge, and he and his companion Franklin head to London on business.
With Arden gone, Alice is left to deal with the visit of Greene, one of the many tenants recently dispossessed by Arden. Seeing that the furious Greene is desperate for revenge, Alice pays him to employ some assassins to kill her husband.
Greene hires the notorious criminals Black Will and Shakebag. These two assassins persuade Michael to leave Arden's door unlocked so that they can kill him in his sleep. A change of heart on Michael's part leads to the failure of the plan, but when the killers threaten to punish him for his betrayal, Michael convinces them to catch Arden as he travels home through Rainham Down.
Back in Faversham Mosby laments the number of people who know of the plan to murder Arden, and decides to have them all killed. When Alice comes to Mosby with her own misgivings, the pair come close to breaking off their relationship. However at the peak of their passion they reconcile themselves once again to their pact.
At Rainham Down, at the very moment when the killers are about to strike, the esteemed Lord Cheyne appears to prevent the act. He invites Arden and Franklin to dinner and accompanies them safely on their way. Foiled once again, Will and Shakebag arrange to ambush Arden on his way to Cheyne's house on the Isle of Sheppey.
The route to Sheppey being obscured by a thick fog, the killers once again miss their mark, so Alice devises a new plot. Meeting Arden as he returns from Cheyne's home, Alice and Mosby will flaunt their relationship in front of him, inciting him to fight. When Arden draws his weapon the murderers will arrive and kill him.
The fight goes wrong though and both Shakebag and Mosby leave wounded. Alice manages to convince Arden that the whole thing was a prank, and sends him after Mosby. The two make peace and Arden invites Mosby to dinner. Meanwhile the murderers agree upon one last scheme..
Mosby distracts Arden with a pre-dinner game of cards. Will and Shakebag creep from a hiding place and finally succeed in murdering the unsuspecting Arden. The killers hide the body, but in all the confusion evidence is left in abundance. When Cheyne and the watch unexpectedly appear. the murder is discovered and the guilty parties are sentenced to death.