This week's episode had some shocking reveals — before plunging us all into the dark again.

One murderer was revealed, another hinted at, and despite Morton telling Sheriff Dan he was going to leave soon, after that shock ending I have a feeling he's not going anywhere.

Here's what we learned this week:

1. "Liam Sutter, 10 years old, hacked a grown man to death." That's right — apparently the murderer that tore poor Charlie Stoddart to pieces was little Liam Sutter, who thwacked the Professor with a breadboard before going to work with potato peeler, knife and cleaver (ouch). The discovery of a child's fingernail inside Charlie's body led to some hyperbaric chamber questioning and the sinister line "I had my hands inside a man". Kudos to Darwin Brokenbro for playing creepy murderous kid so well.

2. But even though the killer's been unmasked, thanks to a handy flashback, the big reveal doesn't make any sense. Liam seems to have been controlled by something/someone, judging by his glazed expression and the whooshing sounds and faint voices from the flashback. He seems to flick in and out of it, too — he went from attacking Charlie to crying "doggie!" and grinning, then during the chamber questioning he went from one word confessions to crying for his mother.

Darwin Brokenbro as Liam Sutter
Darwin Brokenbro as Liam Sutter

3. Despite attempts at being pally, Sheriff Dan and DCI Morton are still at loggerheads. The scene in the morgue, where poor Charlie's demise was described in graphic detail, almost seemed to show them working together. It seems the Sheriff has been forgiven for his attack on Frank. When Morton told Dan about collecting body parts after the Lockerbie plane crash, Dan's bewildered face revealed how much of a small-town cop he really is, and it felt like he was finally starting to respect his British colleague. Then out comes the recording of Henry, and Morton tells Dan he doesn't believe his mercy killing story. Bridges burned.

4. Henry still thinks there's something else going on. If only he could stay sober long enough for people to take him seriously. I think Henry definitely knows more than we think — despite his more erratic moments he was the first person to bring up why Liam killed Charlie, instead of just pulling a confused face like everyone else. His concern for Jules Sutter was sweet (and seemed to always involve an offer of clothing) but then came his discussion with the taxidermist about shamens and spiritual protection. What?! Clearly, between the strange trance Liam falls into and Henry's belief there's something more paranormal going on, Fortitude is taking strides into the supernatural. I just hope the series doesn't get a bit daft as a result.

5. Something went down in Pettigrew's old room, now conveniently occupied by Morton. I jumped out of my skin when Elena first passed the doorway, convinced it was that scary Russian security bloke Max told Morton about. Elena looked like a rabbit in the headlights when he started asking about carpet changes and blood stains — nothing gets past that man! Was Pettigrew killed there then fed to the polar bear? Was the 'mercy killing' all a set up, to provide a cover story?

Michael Gambon as Henry Tyson; Richard Dormer as Dan Anderssen
Michael Gambon as Henry Tyson; Richard Dormer as Dan Anderssen

6. Elena is full of secrets. It's not surprising she can conceal information, considering she never told police who actually killed the man she was jailed for murdering. What is going on with her and Sheriff Dan? Now we understand why he protected her secret with the Governor — she's clearly got some dirt on him, and I think it's Pettigrew-related. Hence why she looked so panicked when Morton questioned her. Dan looked so thrilled to see her when she approached him on the dock, before she shot him down. "You're bad. A bad Sheriff." Currently all signs point to Dan offing Pettigrew in his hotel room, and Elena either helping or catching him at it.

7. Ronnie has lost it. Carrie is now the parent — after she demanded to go home, her tears were soon replaced by Ronnie's pleading and sobbing, while she gave in and hot-wired the snowmobile. His erratic changes in mood suggest some sort of personality disorder — and Carrie seems to have seen it all before. Perhaps even gone on escapades like this before, how else would she be so adept at hot-wiring the snowmobile? But her tired, cold, snow covered face made me wonder how long they can go on like this, nicked snowmobile or no nicked snowmobile.

8. Frank finally seems to feel guilty. After refusing to believe Dan about Liam's murdering capabilities (a denial repeated by Trish, too) and being released from the police station, the consequences of his selfish actions seemed to hit Frank all at once. Finding Jules drunk and passed out on Liam's bedroom floor, curled up on his bedsheets, seemed to be the final straw — Frank finally wept for the family he's destroyed. Elena seems to be sharing the guilt, too, although I did wonder how she managed to just stroll in to the research clinic and straight to Liam's room. Security, anyone?

9. Creepy feeder Markus has Shirley just where he wants her — weak and reliant on his care. His stern expression after she refused the soup was a bit creepy — as was the line about there being 'nothing left of her'. There was a brief but interesting pan down the pictures on Shirley's mirror too, did you spot them? There seemed to be before and after pictures — Shirley appeared to be a happy, healthy size in the before shot (although it was only of her face) and the contrasting after shot was shocking.

Darren Boyd as Markus Huseklepp
Darren Boyd as Markus Huseklepp

10. We now know who the mystery bloke snooping around Charlie's house was. The guy lurking about in episode three is called Yuri, and he's apparently head of security in a nearby Russian mining town. Which makes me think this all comes back to the ice hotel, what Pettigrew discovered, and Charlie's objections to the project. What is under that ice? Part of me wonders if it was the mammoth, perhaps originally discovered by Pettigrew before Ronnie stumbled across it. Speaking of the mammoth, that defrosting corpse is looking seriously disgusting now. Jason, mate, stop getting mad about the missing ivory and concentrate on the rancid mammoth water/blood running into Fortitude's drainage system...

So there you have it. Some answers given, but ultimately we're left with more questions and confusion. And the preview clip of Morton arming himself in next week's episode made me instantly nervous.

What did you make of this week's episode? Share your thoughts in the comments below.