*Major spoilers for Line of Duty episode four below*
For the first 40 minutes or so, viewers were treated to a slow, methodical build-up, with a lengthy interview scene involving the guileless Det Supt Ian Buckells (Nigel Boyle) opening the episode.
Meanwhile, the investigations into the murder of Gail Vella (Andi Osho) and corruption inside the Hillside Lane police station continued to inch forward at a crawl.
But then, after a break in the case sent DS Steve Arnott (Martin Compston) and co to revisit a figure from the series’ past, the episode exploded into action, as a police convoy was attacked in a high-octane shootout (not for the first time).
The episode ended in a cliffhanger, with AC-12 discovering that DCI Jo Davidson (Kelly Macdonald) shares DNA with someone the unit has encountered before – but who?
Many fans have turned into sleuths themselves to try to figure out who the relative is.
See the best reactions to the episode, below…
Many fans had fun with the show’s catchphrases - most of which come from Adrian Dunbar’s Superintendent Ted Hastings.
And the show’s sometimes ludicrous plot...
It’s fair to say, fans are pretty hooked...
Line of Duty airs at 9pm on Sundays on BBC One.