For the unitiated, mudlarking is the practice of combing river banks for interesting artefacts that may have washed ashore. For Clem and her friends, it’s treasure-hunting and story-finding, and in The Thames and Tide Club by Katya Balen, we join them at a time of chaos and calamity on London’s famous river. Only the young mudlarkers can save the day, in an aquatic adventure that will see them encountering pirates, a ballgowned porpoise named Barbara, and an underwater branch of the famous department store, Shellfridges.

It begins on a Saturday morning of notable meteorological peculiarity. The sky is purple and the Thames is whirling and frothing, although there isn’t so much as a whisper of wind. As Clem and her pals, Ash and Lark, head to their weekend mudlarking session, they’re accompanied by ominously bubbling drains and rising water. Undeterred, the doughty trio go on to amass several clay pipes, a muddy 10p piece, a swirled glass bottle, and what looks like a twisted metal ring. One of these objects will prove to be of the utmost importance.

As days pass, the Thames turns into a raging torrent, leaving Tower Bridge ‘swaying like a dandelion in the wind’, and causing all the loos to explode at Buckingham Palace. It’s almost as if the river itself is in the grip of an almighty tantrum.

It’s down to our riverbank heroes to save the day, with some timely magical assistance and the knowledge that the river gives us both things we must protect and things we must return.

A Carnegie Medal-winner whose books are undoubtedly destined to become modern classics, Balen delivers a unique and lively tale, ripe with invention and humour. Subaqueous London is a watery replica of the city above. Visit St Paul’s Clamthedral and Codvent Garden. Don’t forget your Oyster Card!

An environmental message is delivered with the lightest of touches, in the first of a gleefully imaginative series for little bookworms.

The Thames and Tide Club by Katya Balen is published by Bloomsbury Children’s Books, 160 pages.