OK this is where I'm up to so far.
Nanna goes to the flat thinking she is actually meeting Troels again. We have only his word for it that she got fed up with him. I think Morten has logged in as Faust and arranged to meet her in the flat. Hence her excitement - Troels' face is everywhere and she's flattered. Morten attacks her and then bundles her into the car and takes her to the woods. He leaves the flat as it is, so that Troels will be implicated. Morten thinks that he will be the natural successor to Troels, but the fact is he doesn't have the charisma that's necessary for the job. He feels he's doing all the work for Troels and Troels is just taking the benefit. They have known each other twenty years and massive resentment has built up.
Nanna runs away from Morten through the woods. We see that happen at the start of episode 1 - by the way I think it is Nanna, not another girl, who's being chased. However, we assume she's caught. I think she gets back to the car before he does and drives off, leaving Morten there. He has to walk back, hence his need for new shoes.
In the meantime, Nanna phones her father at the garage and the dad's little mate answers the phone. He gets in her car and drives her to the new house. He keeps her there for two days 'taking care' of her. He's jealous of her affair and drowns her.
The necklace she's clutching is one he'd bought for her.
Now I KNOWN this leaves a lot of loose ends - the trips to Latvia, etc. And I do think that Ria's dad is behind the setting up of Troels.
Tell me what you think!