The supernatural drama, which stars Phil Glenister and Christian Cooke, began strongly with around 5.8 million but went on to lose viewers in every week of its six-episode run.
Demons was beaten on Saturday by Lottery show In It To Win It, seen by 7.75m (33.6%) from 8pm.
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Casualty pulled in 6.79m (29.7%) for BBC One from 8.50pm, then comedy The Old Guys put in 3.75m (17.2%). ITV1 had 4.07m (18.8%) for a two-hour Midsomer Murders rerun.
A repeat of BBC One's Charles Darwin and The Tree Of Life brought in 1.73m (7.5%) to BBC Two in the 8pm hour, then documentary Iran and the West - about the Iranian Revolution of 1979 - interested 1.31m (5.8%).
Channel 4 had 1.28m (5.6%) for a repeat of Grand Designs at 8pm, then a screening of the 2003 remake of The Italian Job kept 1.66m (7.9%) until 11.10pm.
Five's NCIS put in 1.19m (5.2%) from 8.40pm, after which a new episode of CSI: New York appealed to 2.2m (10.4%).
BBC One was the clear leader in primetime, with an average audience share of 27.1% to ITV1's 18.7%. BBC Two was third with 7.1%, followed by Channel 4 with 6.3% (+1: 0.5%) and Five with 5.6%.
Ratings data supplied by Attentional