I got it!!
Or at least I got the PDF. The physical book is pre-ordered and I’ll await it too.
So, it’s more a straight chronicle than just a sourcebook for London. The chapters detail episodes of a storyline running through - and the overview is about the players bringing about the resurrection of Mythras, a previously deceased Prince of London, with the main antagonists being the Second Inquisition that seems to be in control of the city now. It’s set in 2012 at the start. There is a map in the back, although I might invest in an A-Z of London anyway for reference. It suggests the chronicle is sandboxy, so there is probably plenty of storyline expansion. The art is excellent, and the layout fine with me. Its 266 pages, so a bit bigger than the Camarilla and Anarch books, but not as big as the corebook.
It has pregens included and, like with The Monsters intro-scenario, I think it’s going to be a game where you’ll probably want to use them rather than generate your own. I’m not sure yet, but in The Monsters, the plot points were very much centered on the characters backstories. As such, I think the ST will need to read the book carefully if they are to integrate difference characters. Notably, one of them is a Hecata Clan vampire - which are due to be detailed in The Onyx Path’s upcoming Cults of the Blood Gods book (and maybe the Players’ Guide?). There are five of them in total - Tremere, Nosferatu, Brujah, Venture and Hecata.
I’ll probably wait for the book before I consider when and how I will play it - but it looks good to read already.