***** S13E01 Endangered Species
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Frost struggles sharing his house with trainee DC Robert Presley (Blake Ritson), who is romantically pursuing a WPC. Criminal Kevin Flangan escapes prosecution due to a lack of evidence, but is forced to turn to Frost for help when his life is endangered. Flanagan admits he was helping Vietnamese smugger Lahn Loc illegally store exotic and endangered animals at his farm, as part of an international animal smuggling ring, but when it was discovered that Flanagan and Loch were keeping money for themselves, the ringleaders had Loch executed. Scotland Yard and HMRC investigators insist that Flanagan is released, against Frost's wishes, so he can unwittingly lead them to his bosses, but the inadequate surveillance loses him while Flanagan is in the Shawcuts pet superstore. His superior, Dennis Prior (Anton Lesser), encourages Flanagan to leave the country, a pretense to have him willingly accompany smuggler Colin Edwards so he can be executed. Frost traces Flanagan's death to Prior and Edwards, who turn on their boss, Shawcuts' owner Kenneth Shaw, ending their part of the smuggling ring.

The Harris family are shocked to return from holiday to find the nude corpse of local art teacher Patrick Bartley in their bedroom. A search of his studio yields revealing photos of a female colleague, music teacher Carol Haymarsh, but Frost is more interested in what happened to the house key belonging to the Harris's son, Adam. Frost learns that Adam gave the key to his 15-year-old friend, Malcolm, so he could use the house to have sex with Carol, and when Bartley found out, he blackmailed her for sex in what he believed was Malcolm's house. Carol states she resisted his efforts and broke his nose, before he died of a heart attack. She is arrested for her inappropriate relationship with Malcolm.