The Mark of the Plague by Kevin Sands

This is a second in a series that began with The Blackthorn Key.  In this one Christopher is living in his old master's workshop while plague rages through London.  Christopher wants to help, but since he has no master, and is still an apprentice, he is not allowed to sell medicines. He and his friend, Tom, barely get by. One day Christopher hears about a strange "prophet" who is going around town foretelling who will get the plague next.  Christopher soon begins to wonder what and who the "Prophet" really is and what connection he might have to Christopher's old master.  His snooping brings him, Tom, and their new friend, Sally, into terrible danger.

I liked the first Blackthorn Key book and I may like this one even better.  It has the puzzles and well crafted mystery of the first book, without as much violence. Christopher, Tom and Sally are all great characters with wonderful chemistry. The details about the plague are interesting, and,as with the first book, the historical and scientific facts seems to be well researched. (529 p.)