1. IS SHE A KILLER?

We spent the whole of series one wondering if Friel’s Marcella was a murderer. There was certainly plenty of evidence to suggest she wasn’t exactly squeaky clean.

After finding out her husband Jason (Nicholas Pinnock) had been having an affair, she stormed round to mistress Grace’s home to confront her.

The next thing we know, Marcella is naked in the bath and covered in blood, while Grace, right, played by Maeve Dermody, is missing – later to be discovered dead in the woods.

In the end Marcella was not the killer, just the person who moved Grace’s dead body… as one does.

But she came close to killing Grace’s murderer Henry, bagging and tying him like his own victims and only coming round from her fugue state just in the nick of time to save him.

Every time Marcella has another blackout she commits a violent act – so all we really know about her is that she is unknowable.

When the fog descends she could be capable of anything, even killing. And that, of course, is what makes this so gripping.