Very tight and square with flat spine - this looks new/unread. No stamps, marks or writing. Age-tanning is very mild and uniform - less than expected for its age.

Flandry of Terra (1965) - a novelet, a novella, and a short novel featuring Captain Dominic Flandry. The 2 longer pieces had previously appeared in book form as halves of Ace-Doubles in 1960 and 1961.

"The Game of Glory"
"A Message in Secret"
"The Plague of Masters"

"The Game of Glory" first appeared in Venture March 1958.
"A Message in Secret" - first appeared (with this title) in Fantastic in 1959, and was re-titled to Mayday Orbit when it was half of an Ace-Double in 1961.
[Captain Sir Dominic Flandry becomes stranded on the planet Altai - and must help win a revolution so he can get a distress signal off. ]
"The Plague of Masters" was serialized as "A Plague of Masters" in Fantastic in 1960, then re-titled to Earthman Go Home! when it was half of an Ace-Double in 1960.
[The planet Unan Besar was hospitable to man, except for a particular strain of bacteria which was everywhere. Unless you got your antitoxin pill from Biocontrol, you would die painfully in 30 days. When Captain Sir Dominic Flandry decides to poke around on a whim, he promptly runs afoul of the tyrannical Biocontrol government, and barely escapes. Hunted and on the run, he must find an Underground and intrigue his way into finding out what this planet had to hide, and bargain for his life 30 days at a time - with just his wits. But Flandry lives for intrigue, and the profits to be made that way…]

In my opinion, Imperial agent Dominic Flandry is the most interesting character that Poul Anderson came up with, better even than the wily trader Nicholas van Rijn. After several short stories from 1951 up, and 3 Ace-Double halves 1959 to 1961, this book and another collection from Chilton (both in 1965) were the first attempt to form a unified and chronological set of the "Flandry" stories. (It just took 15 years for paperbacks of those Chilton collections to come out.) Later books written took place between or before these, which is why there is a "Chronology of Technic Civilization" included in the Ace volumes - which also show that the "Flandry" stories come later in the same timeline as the "Nicholas van Rijn" stories and novels. I recommend this and Agent of the Terran Empire (1965) as good introductions to Flandry - even though they are from the middle of the series by internal chronology, they contain the earliest written stories.