It was always shaping up to be a thoroughly gripping episode and viewers who turned on BBC1 to see Sunday's Line of Duty were left panic stricken from the get to go thanks to an ominous introduction from the channel's announcer.
Last weekend's third episode proved to be the most dramatic of the third series so far with another potential clue to who H could be and a dramatic car crash orchestrated by returning character and the never to be trusted Ryan Pilkington in a bid to silence key witness Terry Boyle, which left another officer dead.
One of the most deeply concerning things about the new series is Steve Arnott's health battle which, while bubbling below the surface of some of the more dramatic storylines, has given Line of Duty viewers real cause for concern.
And the BBC announcer's intro to episode 4 on Sunday did little to settle any nerves as he said: "We've all been doing it...we've all been trying to guess what's going to happen next and finally, now on BBC1, with some violence and some scenes you may find upsetting, let's find out."
Immediately reacting to it on Twitter, one fan posted: "...scenes people might find upsetting..... This doesn't sound good" and another posted: "Let’s see what jaw dropping moments are in store for us tonight!"
A third commented: "i’m so stressed, if anything happens to steve or kate i’ll cry."
Steve's real life alias, Martin Compston already had viewers suitably hyped for Sunday's instalment when he took to Twitter on Saturday to post: "Tomorrow’s the big one episode 4!
"On paper one of the best @jed_mercurio has ever written, if we deliver what was there potential to be a classic.
"Like to give a shout out to the young team Shalom and @gregorypiper98 who give outstanding performances in the midst of the madness"
