The spy series' 9pm outing, starring Richard Armitage, logged 4.5m (19%) compared to last week's 6.01m (24.8%).
ITV1's third instalment of car crash drama Collision, meanwhile, maintained 5.97m (25.2%) across the same hour. The first two drew 7.5m (30.4%) and 6.32m (26.5%) respectively.
Andrew Marr's The Making of Modern Britain averaged 2.49m (10.5%) on BBC Two, while over on Channel 4 observational documentary The Family logged 1.82m (7.7%).
Earlier in the evening, Waterloo Road won the 8pm hour, putting in 5.19m (22.9%) and ITV1's An Audience With Donny and Marie attracted 4.23m (18.7%). BBC Two's Natural World had 2.43m (10.7%) and Britain's Best Brain on Five interested 602k (2.7%).
Channel 4's Country House Rescue managed 1.74m (7.7%) at 8pm, before the latest instalment of True Blood drew 1.14m (7.1%) at 10pm.
Overall, ITV1 led primetime with an average share of 24% to BBC One's 21.1%. BBC Two was third with 8.4%, followed by Channel 4 with 6.4% (+1: 0.7%) and Five's 3.4%.
ITV2's episode of Gossip Girl, meanwhile, was seen by 116k (0.5%) at 8pm.
BARB ratings data supplied by Attentional