Expiation is episode 4 of series 1. It first aired on 4 March 2007.
Rachel and Hugh Mallory pack off their two daughters to the car pool for school. The kids are being driven by David and Louise Hayward, close friends of the Mallorys; David and Hugh are partners in an optometry business. Hugh comes home from work and engages in some chit chat with his neighbor, Stephanie. Together they enter the Mallory home and find Rachel—dead! Lewis and Hathaway investigate and find some extremely odd things about the Mallorys and the Haywards. Like how Hugh used to be married to Louise, and David to Rachel, before the couples swapped partners. When the temporary pathologist filling in for Dr. Hobson writes Rachel’s death off as suicide, Chief Innocent orders Lewis to close the case.
Gallery
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Video clip
Extras
Behind the scenes and interview with James for Lewis.
Links
Lewis, Morse and Endeavour Archive website
Synopsis by tvtropes