That fucking eyesore still dominates the skyline, same as it did the last time he was here, but the city feels different, somehow. He doesn't realise he's been holding his breath until he steps off Charing Cross Road and into the Leaky -- being run (at least for tonight) by someone he doesn't recognise, but who is definitely wizarding.
There are any number of places he should visit -- the Estate House, their flat, Alphard's portrait at the Wenlock Museum, the hospital -- but he can't be certain how long he can access this version of the Wizarding World, and his top priority is catching up on nearly thirty years of advances in therapeutic magic.
Just as the line that separates the study of Defence Against the Dark Arts from the study of the Dark Arts themselves has been extremely thin and... fluid over time (depending on who's running the Ministry), so has the line that separates the study of how to heal people from the study of how to hurt them.
When he can't find what he wants at Flourish and Blotts, Sirius abandons Diagon Alley for MacAbre's in Knockturn Alley, pulling volumes down from the shelves and having one of the staff ferry them over to a private reading room (in case the books go missing between here and Margate).
He's a couple of hours into flicking through the different books when he comes across a reference to a rescinded defibrillating charm, explained in greater detail in an earlier volume...
...which MacAbre's doesn't have. But which he's told should be available in Flourish and Blott's back stock, since it dates back to when that particular journal was deemed fit for public circulation (1986 -- right in between the first and second wars, when Ministry complacency was at an all time high).
Hoping that his books will still be there when he returns (if he's able to return... but he's left instructions as to where the books can be sent to, just in case) he wanders back to Flourish and Blotts, hoping he doesn't have as much difficulty attracting one of the sales staff as the last time.