Alison Rowat reviews The Replacement (BBC1), Top Gear (BBC2), and The Nightly Show (ITV1)

Set in a glossy magazine Glesga of swish interiors and honey-coloured tenements, The Replacement is the story of architects Ellen and Paula. Ellen (Morven Christie) went off on maternity leave in the first episode, leaving Paula (Vicky McLure) to take over as her temporary stand-in. This, as anyone could have told Ellen, was asking for trouble. McClure (This is England, Line of Duty) commits grand acting honours’ larceny in everything she is in, and if it wasn't for Christie being on top form on her home turf, Fingers McClure would be off with all the prizes here too.

Joining the ranks this week was baby Leah, who made an appearance after Ellen went into labour early. The little miss, that's Leah, not Ellen, delivered a thoroughly convincing turn as a newborn, complete with RADA-standard bawling when left unattended in a car while mum continued her transformation into Lieutenant Columbo. Ellen is convinced there is something rum going on with Paula, other than her suspicious carrying of not one but two designer totes (talk about totes-upmanship). Even tiny Leah, still wet behind the ears from her water birth, seemed to know how spectacularly daft the whole thing was, but she ploughed on gamely. Those nappies won't buy themselves.

Amateur ‘tec Ellen appeared to be making good progress in the case, using every ruse in the book to gather clues, as when she wanted to have a nosey around someone’s bathroom and excused herself by saying: "I think I might have just burst my stitches. I'm just going to have a look." Beat that, Peter Falk. As a rule, when characters meet lines like: "It doesn't make any sense!” with the answer, “Who says it has to make sense?”, it should be plain to all we've bought a one-way ticket down the rabbit hole.

It is anyone’s guess what epic silliness will happen next, which is as it should be going into Tuesday's finale. Will Ellen or Paula turn out to be Glenn Close? Are the men really as nice as Glen Michael of Cartoon Cavalcade fame? And after the tension induced by this psychological thriller, could we all do with a nip of Glenmorangie and a nice lie down?

Definitely no drinking on the new model Top Gear as it returned for a second series, though given the disastrous first season sans Clarkson and with Chris "WHY ARE YOU SHOUTING?" Evans, you could perhaps have forgiven Matt LeBlanc and co-presenters Chris Harris and Rory Reid for wanting something stronger than a cuppa before setting out.

As it was, they relied on the old formula of posing as three ordinary blokes in dad jeans who could not quite believe they were being paid to drive dream cars. All that, and Scots actor James McAvoy turned up as the star in the reasonably priced jalopy (no one used the segment's original title, presumably for copyright reasons). Escaping from the shadow of the ginger shouter suits LeBlanc, and his sidekicks seem as if they might grow on a viewer, like mould. Everyone was engagingly eager to please, but it was all a bit Sunday afternoon outing to the garden centre in a people carrier. One suspects it will not impress those Clarkson fans whose idea of a good time is a fumble in a sports car followed by a post-drive ciggy and some casual racism at the locals’ expense.

ITV’s The Nightly Show, an attempt to import the US format of late night comedy and chat, continues its slow walk towards the execution chamber. This week comedian John Bishop took over from “comedian” David Walliams. The Scouser could hardly do worse, and he didn't, but come Tuesday the desperation was such that he brought his two bull terriers from home in a bid to win hearts. Honestly, who let this dog out?