The programme, which stars Orla Brady, Patrick Baladi and Joanna Lumley, averaged 3.98m (17.7%) for BBC One from 9pm. An additional 147k (0.7%) tuned in on BBC HD.
Mistresses beat Police, Camera, Action! in the 9pm hour, after the factual crime series pulled in 3.27m (14.5%) for ITV1.
In The Line Of Fire, a Tonight special on gun and gang crime in the UK, attracted 2.43m (12%) to ITV1 between 7.30pm and 8pm.
A new episode of Celebrity Masterchef brought in 4.28m (19%) for BBC One in the 8pm hour, up 120k week-on-week.
EastEnders secured the biggest primetime soap audience, with 8.04m (39.3%) watching on BBC One between 7.30pm and 8pm. A further 993k (5.5%) caught the episode when it was repeated on BBC Three from 10.30pm.
Five's The Hotel Inspector averaged 1.8m (8%) in the 9pm hour, up 340k week-on-week.
The latest episode of Big Brother brought in 2.29m (13.5%) for Channel 4 between 10pm and 11.10pm. The programme took an additional 189k (2%) on Channel 4 +1.
Location, Location, Location attracted 1.59m (7.1%) to Channel 4 in the 8pm hour and 218k (1%) on timeshift. It was followed by Undercover Boss, which brought in 1.66m (7.4%) and 241k (1.3%) on Channel 4 +1.
Wainwright's Walks: Coast To Coast averaged 1.28m (6.9%) for BBC Two from 7pm, before Mastermind: Champion Of Champions took 1.9m (9.3%).
Natural World pulled in 1.74m (7.7%) for BBC Two in the 8pm hour, and it was followed by Victorian Pharmacy, which took 2.01m (8.9%) from 9pm. A new series of comedy Getting On opened to 1.22m (6.1%) between 10pm and 10.30pm.
On Five, Fifth Gear secured 410k (2%) between 7.30pm and 8pm. It was followed by The Man Who Moves Buildings, which took 705k (3.2%) in the 8pm hour.
Later on Five, documentary Crimes That Shook The World attracted 882k (5%) in the 10pm hour.
Overall, BBC One won primetime with a share of 21.5% over ITV1's 19%. BBC Two came in third with 7.8%, followed by Channel 4 with 7.6% (+1: 0.8%), and Five with 4.4%.
Elsewhere, a DEC Pakistan Flood Appeal secured the biggest multichannel audience of the evening, with 1.02m (5.2%) watching on BBC Three between 10pm and 10.30pm.
ITV4's live coverage of Liverpool's Europa League win against Rabotnicki averaged 947k (4.4%) between 7pm and 10pm.
The first semi-finals of America's Got Talent pulled in 385k (1.7%) for ITV2 from 10pm and 149k (0.7%) on timeshift.
BARB ratings data supplied by Attentional