Last night's show, the seventh instalment of an eight-part series, drew a 19.7% share of the audience between 9pm and 10pm.
In the same slot 'Spooks' only managed 4.4m viewers and an 18.5% share.
However, the largest audience of the night went to ITV's live coverage of Liverpool's must-win Champions League group stage qualifier at the Stade Velodrome in Marseille.
The game, which Liverpool comfortably won 4-0, was watched by 4.8m viewers and a 20.5% share, between 7.30pm and 10.30pm.