Peter Saxon* - The Case of the Missing Bullion - Howard Baker - 1969
Due to illness I wasn't able to review this while it was fresh in my mind.
I recall it well enough to say it was a cracking little tale that sees Blake pitting his wits against a villain with aristocratic pretentions known as The Gent as a routine search for a missing young woman turns into something more sinister.
The Gent is a great creation ; urbane, courteous and ruthless to the point of psychopathy.
Blake is portrayed as polite and respectful to the people he meets, inclined to make more measured judgements than his assistant, Tinker. Unusually, he is portrayed as rather philosophical about the march of 1960s modernism even when one suspects it doesn't meet with his approval.
Generally it is reasonably well-written but with attempts at period flavouring (much talk of "swinging chicks" etc). Occasionally the writing inadvertently invites mockery ("she didn't like the way he glanced at her knees" and "she had never liked swarthy men with very thin moustaches"), but this is rare.
I am not a huge fan of 5th series Blake but I can't imagine many fans of the great man being disappointed with this.
* On the cover the book is credited to Peter Saxon, a house pseudonym. However, Peter Gordon is credited as author on the half-title page, title page and reverse of the title page. Blakiana credits it to W Howard Baker. I'm no expert, but my money is on the mysterious Peter Gordon.