I’ll be honest with you. My hopes weren’t high for new six-part drama After the Flood. ITV drama is a hit-and-miss affair – increasingly the former, but not yet often enough that you can approach an evening’s viewing with unassailable confidence in the investment you are about to make – and the publicity made this one sound like a standard police procedural, with added water.

My hopes do not noticeably rise in the opening scenes, which does indeed contain a lot of added water as a river bursts its banks and floods the nearby town. The local police leap into action. “Let’s do all we can to help,” says their sergeant (Nicholas Gleaves), which makes you fear for the script and the townspeople’s chances of survival. Soon PCs Joanna Marshall (Sophie Rundle) and Deepa Das (Tripti Tripuraneni) find themselves losing the slightly bathetic struggle to save an infant from being carried away by the waters (you shouldn’t try these things without a Hollywood budget; the waters are never quite dramatic enough, the baby always too rubbery). They are metaphorically saved, and the baby, literally, when a passing stranger dives in and rescues it before being carried away himself. As the days wear on, he is presumed by Jo to have drowned.

Then … well, then the dramatic set piece – ending with the revelation that Jo is pregnant (this is her last day on active duty) – is over and After the Flood gets really good. It settles into the aftermath of the disaster, introduces us to folk, conjures a real town and real relationships swiftly and convincingly. You understand within a few minutes why the show has attracted the likes of Lorraine Ashbourne (absolutely wonderful as always, this time as Jo’s widowed mother, Molly), Philip Glenister (so far just as a helpful local man with a tractor but with no doubt more to do) and Rundle to its cast. Peripheral characters – such as the old couple who have known Jo for years and decline her offer of help with a detailed account of their flood preparations and the state of their bowels – are as credible as any others. It is a perfectly rendered community and you barely need the imminent murder mystery to keep you watching.

But murder mystery there is (on top of, and possibly tied to, the maybe-drowned baby-saviour), sparked by the discovery of a man’s body in a lift in an underground car park. At first he is presumed to have been caught by the rising water, until the postmortem reveals that he was dead for at least three days before that. Jo, the first officer on the scene, becomes increasingly interested in the case, and remains so despite a nice, unexpected twist which hampers her involvement. Then we end on a pleasing cliffhanger which should seal the deal on viewers coming back for more next Wednesday. This is a series rightly confident enough to have gone for old-school weekly releases. January is the perfect time for deferred gratification, after all.

The broader backdrop is the climate crisis. After the Flood is about how big global changes play out in microcosmic terms. The local councillor’s flummery when confronted (mostly by Molly – do not mess with a community linchpin who is distracting herself from grief) about the lack of sandbags, sirens and other resources that might have mitigated the dangers is emblematic of international inertia in the face of looming planetary catastrophe. The tragic failure of the old couple’s preparations shows the limits of what we as individuals – or even individual countries – can do. This message would be depressing enough to cause viewers to desert the show in droves, were it not folded into a good story playing out among even better characters, and made extra palatable by the rare and delightful sense that you are unexpectedly being served something much, much better than it needs to be.