The fifth show of a six-part series, starring Amanda Burton, attracted a 23.8% share of the audience, according to unofficial overnight figures.
The return of ITV's long running crime drama has been a big success for the broadcaster, with the programme regularly beating its competition in a tough 9pm slot.
The series is up against the BBC's new travel series, 'Mountain', in which comedian Griff Rhys Jones journeys across the UK's highest peaks.
'Mountain' was watched by 4.8m viewers and a 21.5% share, while on Channel 4 in the same slot, 'Big Brother' picked up 3.8m viewers and a 15.1% share.
Earlier in the day, a controversial win by British Formula 1 driver Lewis Hamilton drew 3.2m viewers and a 36.7% share in a 12pm-3.30pm slot.
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