The 16-year-old crime drama, starring Emilia Fox, pulled in 5.64m (24.5%) in the 9pm hour, down just over a million viewers on its 15th series opener in April.
Losing out by some margin, ITV1's three-part thriller The Last Weekend premiered with a disappointing 3.2m (13.8%) and 212k (1.3%) on +1.
Celebrity Big Brother held 1.69m (7.3%) and 198k (1.2%) on +1 over on Channel 5, while Lee Evans's stand-up amused 1.44m (6.4%) on Channel 4 (+1: 370k/2.2%), and Toughest Place to Be a Miner interested 1.58m (6.9%) on BBC Two.
BBC One's Countryfile was the night's most-watched show with 5.78m (27.1%) at 8pm, over double the audience of The Cube's 2.77m (13%) on ITV1 at the same time.
Meanwhile, Once Upon a Time secured 958k (6.4%) for its latest episode, 'An Apple Red as Blood', while Come Dine with Me served up an average of 1.12m (5.2%) for Channel 4 (+1: 156k/0.7%), and 1.16m (5.5%) watched BBC Two's culinary offering of Exploring China.
Overall, BBC One swept up the peaktime crown with 24.1% versus ITV1's 13.2% (+1: 0.6%). BBC Two earned third place with 5.8%, ahead of Channel 5's 4.8% (+1: 0.6%). Channel 4 and BBC Three tied in fifth place with 4.4% (C4+1: 0.7%).
The Only Way Is Essex topped ITV2's night with 970k (5.4%) at 10pm (+1: 179k/1.7%), prior to which a repeat of Saturday's X Factor grabbed an impressive 791k (4.2%) from 6.45pm (+1: 239k/1.1%), and The Xtra Factor logged 715k (3.3%) at 8pm (+1: 224k/1%).
BARB ratings data supplied by Attentional