A series book - a spy thriller starring Peter Ward. Never heard of the series, never heard of the author. This is apparently the second one.
It's fairly low-key for a spy thriller. The premise is that (in 1960ish) a contender for the Spanish throne has returned from the gulags of the Soviet Union. Ward must ingratiate himself with his daughter and current caretaker and establish the man's identity, because a serious contender for the throne would destabilize Spain and possibly gain a Soviet presence in Western Europe.
It struck me how much people drank. Barely a page goes by without someone drinking something. Was it socially acceptable for the times, for Spain?
Other than that, it was pretty much by the numbers. No grand masterwork plan, no supervillains, no outrageous technology. It made me think "this could happen", except for the concept of a playboy superspy.