Midsommar (horror film: trailer).
In the movie Midsommar, a couple travels to Sweden to holiday with a buddy and end up attending the town’s odd mid-summer festival.
Heck, have they never seen the Wicker Man?
Yes, of course, a pagan cult is involved and things get weirder and more demonic faster than you can draw a pentagram on the ground using the spilled blood of a Member of Parliament.
If they made this into a TV series, would it be called Midsommar Murders, I wonder?