Scottish Police

Yeah, the ending does seem to fall apart once you get beyond the "shock" of the final twist.

It only kinda works if the pub owners and some of the locals were in on Sophie and Wendy's endgame. Except we know that the one waistcoated guy was killed for body parts. And the Gameskeeper was not involved.

1) Johnners is alive and making a phone call. If it is a fake call, it is only for the benefit of the locals in the pub. If it is a real phone call, we know it is a deception and not to the real police (as he states to Ian) because his tone is quite jovial and he seems to say "I love ya" then definitely "I'll call you back" once he sees Ian. He certainly wasn't talking to Fran (as he also states) because she doesn't mention it to Ian when he later calls her. It wasn't Wendy because Johnners doesn't use that information as a bargaining chip with Sophie while he hovers over the meat grinder. He could have easily said, "if I die, no one outside of the tontine can collect it because that is how Wendy set it up. Go ask him." So it is reasonable to infer that he thinks she killed Wendy and he is not privy to their plan. If it wasn't Wendy he was calling, who was it? Perhaps it was the alibi he was off to arrange when he told Sophie to finish off Ian. It does appear that he had another honey on the side.

2) Ian tells the barmaid to call the "Scottish Police" - which seems specifically particular. But okay. It appears she does, telling Johnners that the polis are on the way. The other patron says with road conditions it should take an hour. So did she call the real cops, the fake Wendy cop or no one at all?

If she called the real cops, and she and the locals were not complicit in the crimes, they would give evidence like the stag party reservation info, Ian's card details, the human sausage grindings in the cooler, a description of a hot bird with the rifle and the one phony cop that arrived within ten minutes to take her away but didn't wait for backup or forensics. Just going with the one dude pulverized in their freezer, there would be a massive investigation. They will say Ian was clearly involved and simply walked off. When tracked down and pressurized by the inspectors, Ian is going to grass everyone up. He doesn't get to just saunter off like a nebbish with an "all is good" phone chat to his sibling. At least ten people are missing and/or been dangerous gamed. So Ian taking an aw-shucks constitutional means nothing. How is that going to look when the authorities question his sister and pull the phone records? If the real police are called.

The barmaid couldn't have faked a call to no one; otherwise no cops (fake or real) would show up. One needed to happen for the twist.

But if her call was to Wendy, telling him that Sophie had arrived - why else would Sophie be there, toting a fully loaded gun? She has to be there and someone has to see her to justify a panda car showing up and hauling her off. But again, once the stag party members are reported missing, they will easily be traced back to the tavern. Even if the locals (they did seem nonchalant when Sophie strolls in packing heat) were in on it, this was the last place the stag party members were seen together. Ian's card puts him there. By not calling the real police the conspirators have time to cover up a lot of evidence to make the scot-free ending work. Cleaning up the equipment, the bodies in the woods, the trashed cars and cottage. They could just play dumb when the actual authorities come around. But still, Ian is alive and wandering around the highlands in a deer costume. I suppose he could feign recollection for his sister's sake. But everyone else needs to be found dead for the tontine to pay out! So they can't dispose of the bodies. They won't find Wendy's body. And Ian has been mercifully left alive.

But again, why bother with the whole fake cop deception anyway. Sophie was a shadowy non-entity before. Now she's a known suspect. Just so you could pick her up in a public location? Why not just kill Johnners in the woods and the two of you scamper off presumed dead and not even a part of it? None of this washes on closer inspection, especially with the second twist and triple-cross and protagonist apathy.