She was portrayed by Trudie Styler in the 1984 BBC adaptation, and by Mary Stockley in the 2004 adaptation from Agatha Christie's Marple.
Being the person behind the double deaths of Ruby Keene and Pamela Reeves, Josie was secretly married to Mark Gaskell, the widower of Conway Jefferson's daughter. Both of them attempted to kill off Conway. Upon learning that Conway planned to adopt Ruby and gave her his legacy, they made the double murder plan.
To achieve this, Mark hosted a fictitious screen test and lured a 16-year-old local girl named Pamela Reeves to the hotel. Josie dressed Pamela, dyed her hair and made her up to resemble Ruby, and then drugged her.
During the bridge play at the Majestic Hotel in Danemouth, where Ruby was presented at the scene, Mark took a break, taking Pamela’s body to Blake's hearth rug, where he strangled her with her belt. Just before midnight, when Ruby went up to change for the exhibition dance, Josie followed her and killed her by injection or a blow.
After the midnight dance, Josie stole the car of George Bartlett and carried the corpse of Ruby, now dressed in Pamela’s clothes, to a quarry and burned down the car. Mark carried the corpse of Pamela to Basil Blake, However, Basil after returning back home from a party while drunk, could not recognized the body or making rational decisions. He then carried the corpse, while still drunk, to Colonel Bantry's library as a prank since he never liked the colonel.
After her investigation, Marple began to doubt Josie's identification over "Ruby's" corpse, which led her to discover that the body in the library, that was originally claimed to be Ruby, was actually Pamela. She then set a trap to trap Josie. Under Marple's advice, Sir Henry soon found the marriage record of Josie and Mark in Somerset House, and persuaded Conway to change his will. At 3 a.m., Josie snuck herself into Conway's house, but was subdued and arrested by the police. Mark soon confessed his crime once Marple finished her denouement.
- In Agatha Christie's Marple, Josie's accomplice is Adelaide Jefferson, who becomes her lesbian lover in this adaptation, not Mark Gaskell as in the novel. In addition, the police trapped Josie after Marple gave her deduction of the case, not before that.
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