"Two hours later, the train slid into Gare du Nord."
Check on Eurostar timetable that it takes just over two hours from St Pancras. It does.
Simple enough - but check a map of Paris to make sure the setting sun would be behind someone on a bateau mouche going past Notre Dame.
Same evening, after a lot has happened:
"See you in the hotel bar at 7.” An hour.
So what time was sunset in Paris in early November? Was there enough time for all that to happen? No. Sunset was 5:30. Not time to nearly drown, be rescued, go home, get changed, have a shower and arrange a meeting for 7 while 7 is still an hour in the future. Change to meeting in the bar at 9.
"The executioner's black hood..."
Look at engravings of numerous executions by guillotine: the executioner is never hooded. Change that.
Oh, and a much bigger issue I noticed - a key character is in Paris in one book and in Russia in another book. At the same time. Not even vampires can do that. Calendar change....
It's easy to think you know what's happening, but important to make sure it actually could happen like that. So this is just a reminder not to be complacent about the lies you tell.
Happy New Year!