The finale episode of the crime drama grew over 500,000 viewers from Wednesday's broadcast, while a further 355k (2.0%) tuned in on +1.
Earlier, an Oklahoma tornado Tonight special was seen by 2.86m (14.8%) at 7.30pm. Paul O'Grady's For the Love of Dogs dipped 200k from last week to 4.74m (21.8%) at 8.30pm (184k/0.8% on +1).
On BBC One, Britain's Biggest Hoarders brought in 2.94m (13.1%) at 8pm, while Question Time was seen by 2.75m (22.4%) at 10.45pm.
BBC Two's coverage of the Chelsea Flower Show continued with 2.53m (11.8%) at 8pm, followed by the documentary The Last Days of Anne Boleyn with 3.02m (13.4%) at 9pm. Watson and Oliver grabbed 582k (3.0%) at 10pm.
Channel 4's new show Fat Family Tree attracted 942k (4.4%) at 8pm. The Hunt for Britain's Sex Gangs secured 1.10m (4.9%) at 9pm (250k/1.4%).
Channel 5's Dan Brown-themed True Story was seen by 1.17m (5.5%) at 8pm. The Most Shocking Talent Show Moments entertained 1.11m (6.7%) at 9.15pm.
On BBC Three, Russell Howard's Good News rose to 893k (4.6%) at 10pm. Family Guy peaked at 661k (5.7%) at 11pm.
On E4, The Big Bang Theory tickled 1.29m (6.1%) at 8pm (516k/2.3%), while How I Met Your Mother brought in 824k (3.8%) at 8.30pm (259k/1.1%).
ITV2's Peter Andre: My Life ended by dropping to 711k (3.2%) at 9pm (183k/1.1%), followed by the final Celebrity Juice of the series with 1.17m (6.4%) at 10pm (296k/2.9%).
BARB ratings data supplied by Attentional