I've not seen it (nor, indeed, even heard of it until now). I've found a couple of links that explained the ending but then I worked out that they refer to the end of the series as a whole, rather to the episode that was aired last night. So I'm not posting them here, as they'll act as spoilers for the following episodes.
I will point out though that the whole of the series (including the two episodes that haven't been aired on conventional TV yet) is already available to watch on ITV Hub. So you can catch up on what you missed last night and find out what happens from thereon as well:
https://www.itv.com/hub/no-return/10a1219