Starring Martin Clunes and Hermione Norris, the ITV drama concluded with 4.12m (17.5%), above Accused's 3.35m (14.2%) for BBC One.
A Mother's Son, which added a further 531k (3.1%) on +1, won the slot despite a poor lead-in from Unforgettable: The Sweeney, which had 2.07m (9.2%) at 8pm (+1: 117k/0.5%).
Still, the two-part thriller lost 350k on Monday's premiere audience, while Jimmy McGovern's Accused shed over 700k week-on-week.
The Paralympics continued to perform steadily on Channel 4, averaging 2.34m (10.6%) for three hours from 7.30pm (+1: 114k/0.6%).
Meanwhile, Person of Interest logged 1.09m (4.6%) for Channel 5 at 9pm (+1: 123k/0.7%), then 1.8m (10.5%) watched Celebrity Big Brother, and the reality show's spinoff Bit on the Side grabbed 657k (7.5%) from 11pm.
Overall, BBC One led primetime with 19.2%, ahead of ITV1's 14% (+1: 1%), BBC Two's 10.4%, Channel 4's 9.6% (+1: 0.6%), and Channel 5's 4.5% (+1: 0.3%).
Jack Whitehall's Bad Education slipped slightly to 851k (4.4%) on BBC Three at 10pm, appealing to a further 357k (10.8%) at the late time of 12.30am. Don't Tell the Bride managed 727k (3.1%) in the 9pm slot.
BARB ratings data supplied by Attentional