Part one of the mini-series, which stars Dervla Kerwan and Genevieve Barr, appealed to 4.71m (20%) on BBC One from 9pm.
The drama comfortably beat ITV's Identity, after the programme pulled in just 3.83m (16.2%) on ITV1 in the 9pm hour, down 1.77m on its debut episode last week.
Earlier on BBC One, Fake Britain took 3.29m (15.8%) between 7.30pm and 8pm, before a Panorama special on the orphans of Haiti averaged 2.26m (9.9%) between 8.30pm and 9pm.
Antiques Master secured 1.94m (8.5%) for BBC Two between 8.30pm and 9pm, and it was followed by Mary Queen Of Shops, which pulled in 2.65m (11.2%) in the 9pm hour. Sitcom Rev brought in 1.51m (7.3%) for BBC Two between 10pm and 10.30pm.
Dispatches: Africa's Last Taboo took 610k (2.7%) for Channel 4 in the 8pm hour and 106k (0.4%) on timeshift. It was followed by documentary special Concorde's Last Flight, which averaged 2.01m (8.9%) between 9pm and 10.30pm, with 214k (1.3%) watching on Channel 4 +1.
Big Brother was watched by 2.09m (15.1%) on Channel 4 in the 11pm hour and 107k (1.6%) on timeshift, before Being N'Dubz brought in 410k (5.6%) and 51k (1.4%) on Channel 4 +1.
On Five, Police Interceptors secured 1.01m (4.5%) in the 8pm hour, before a screening of action film XXX appealed to 1.07m (5.3%) between 9pm and 11.15pm.
Overall, ITV1 won primetime with a share of 21.8% against BBC One's 20.3%. BBC Two came in third with 9.1%, followed by Channel 4 with 6.2% (+1: 0.6%) and Five with 4.2%.
Elsewhere, a new episode of Britain's Next Top Model was watched by 276k (1.2%) on Living from 9pm.
Also in the 9pm hour, documentary Rich Hall's Dirty South pulled in 565k (2.5%) for BBC Four, which was fifth largest multichannel audience of the night.
BARB ratings data supplied by Attentional