Not sure why everyone is complaining about too many plot lines!
Its a "detective" story. There must be any number of real life situations where dectives start off down one avenue of potential culprits only to realise that it is a dead end.
And even more likely when the crucial fact was secret.
I think the spy element and the unlicensed treatment (or whatever it was) was a bit over the top. Could have had, I dont know, illegal whisky distillery or something.
I never suspected the culprit. In fact half the time I couldn't remember who ever one is. These Shetland familes are a nightmare. You almost feel all new borns should be taken into care, because otherwise they grow up with historic family grudges, or mental distress.
But really liked the last scene. Thought it was very well done, and gave Ruth a chance not to be an old grump. But not only was she late (I empathise) but she hadn't made the effort that Tosh had to dress up. (Is it part of the plot that Tosh's clothes always look wrong?)
And as before, that young boy was just brilliant.
re families - dont suppose anyone could draw a family tree of the culprit? I cant quite fit them all in together.