The authors are not shy in recommending the works of others. I won't deny that I was gratified to see my book "Close to Holmes" listed as one of the best topographical guides to Holmes' London (but I assure you that this has not influenced my mark). The book is simply excellent.
Sorry but I simply cannot fault it. 5 pips.
For something similar please look at my review of the book Amazing & Extraordinary Facts: Sherlock Holmes by Nick Utechin