The Great When , Alan Moore (Bloomsbury 978-1-63557-884-3, $29.99, 336pp, hc) October 2024. By now there are so many mystical-magical ‘‘hidden London’’ novels that it’s getting hard to keep up – though admittedly there’s something delicious about the notion that in any great city, you’re only being shown what they want you to see, with the real city available only at certain access points for certain chosen adventurers. In his acknowledgments to The Great When, the first volume of a projected five-novel series called Long London, Alan Moore singles out only Michael Moorcock and Iain Sinclair among antecedents, but there’s little doubt that he’s broadly acquainted with the conventions of the form and fully prepared to place his distinctive if at times familiar stamp on it. As an artist named Spare explains to Moore’s young protagonist about Long London (or the Great When), ‘‘that world, it’s realer than the one we’re in. Our world’s just a shadow next to that, up on the wall of Plato’s cave. If this London is what they call the Smoke, that place is the Fire, you follow me? This ’ere is echo, and that there is music.’’ As if to underline this stylistically, Moore’s narrative shifts into an exuberant, all-italic present tense when we’re in his phantasmagorical version of Long London, and the flood of surreal and expressionist imagery is as intimidating to us as it is to his characters.