The seven-episode series, which is set in a supermarket chain's head office, debuted last week with 3.7m viewers.
Yesterday it started with 3.9m viewers at 9pm-9.15pm but dropped to 3.1m by its final quarter-hour at 9.45pm-10pm.
This gave ITV1 a 9pm-10pm viewing share of 15%, which put it second in the slot behind BBC One with 22.4% of viewing.
BBC One secured an audience of 5.1m with the second episode of Jimmy McGovern drama series 'The Street', which opened last Monday with 5m viewers.
BBC Two managed 1.9m viewers and an 8.2% share with 'The Supersizers Eat ... The Fifties', just ahead of Five, which brought in 1.7m viewers and a 7.6% share with 'The Hotel Inspector'.
Channel 4's animal anatomy series 'Inside Nature's Giants' finished with 1.5m viewers and a 6.5% share. It was seen by another 163,000 viewers on Channel 4+1.
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