The Lynda LaPlante series, titled 'Above Suspicion: The Red Dahlia', bowed out with a 25.2% share of viewing in the 9pm-10pm slot.
Its closest competitor was BBC One, which took a 14.2% share with a repeat of ageing detective series 'New Tricks'.
Channel 4's share came in at 11.8%, including its C4+1 ratings, after 2.9 million viewers watched 'Gordon Ramsay's F-Word'.
'Celebrity Big Brother' continues to do well at 10pm, bringing in 3.2m viewers and earning an 11.8% share.
Back at 9pm-10pm Five lagged the rest with just one million tuning into 'NCIS'. Its 3.8% share was far behind BBC Two's 8.8% for a documentary about canines.
'Horizon: The Secret Life of the Dog' fetched 2.4 million viewers as the documentary strand kicked off a six-part series.
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