THE REPLACEMENT, BBC1, 9pm

PART of the fun in this excellent series has been reading the various theories put forward online as fans dissect the show. I watched the entire series in one go when it was first released to me (there was obviously no way to stop), so I’ve missed out on the agony and anticipation the viewers have been feeling each week.

I was in the chemist last week where some of the scenes were filmed. The staff were discussing it and it was hard not to lean over the Rennies and grab the sales assistants, squealing: “I know how it ends!”

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The story has been so clever and intricate that it’s never been entirely clear whose side we should be on, but everything is resolved tonight with mighty satisfaction. Ellen and Paula come face to face at the opening of the library, with nasty consequences for one of them. Things do get a little melodramatic as we race to the finale, and there are scenes to make a claustrophobe wince, but it’s drama after all, so suspend your disbelief and enjoy.

INSIDE NO. 9, BBC2, 10pm

AFTER last week’s weaker episode, the show is back on form. David is out jogging in his nice suburban street when he spots a black shoe lying by his garden gate. Curious, and it’s not even a grotty old trainer but an expensive leather shoe in perfect condition.

He takes it inside, just in case the owner comes looking, and slowly becomes obsessed with it. How it was lost? Who might it belong to, and how he can reunite it with its owner?

We wonder if David is perhaps unstable or traumatised by something in his past. His wife goes to work each day but he stays at home. Is he a house husband or perhaps mentally unwell? Has something awful happened to him and the shoe obsession is just a symptom of his illness?

This is a brilliantly slow, creeping and sinister episode.