Space Mercenaries by A. Bertram Chandler is the sequel (tho easily stand-alone) novel to The Empress of Outer Space, and continues the adventures of Mrs. Trafford, the ex-Empress of a galactic empire.
Irene Trafford, nee Smith, has, along with her husband (an ex space navy officer), Susanna her ex-lady-in-waiting, Tallentire a willing gunnery specialist conscript and Mr. Metzenther, a psionic radio operator and telepath, taken to the spaceways aboard her private pocket battle cruiser, setting up in business as a well-armed tramp merchantman.
The happy crew aren't in business long before they are approached by a shady representative of GLASS, the Galactic League Against Slavery and Suppression, a private organization that has its tentacles into just about everything going on in the galaxy, including an interest in a human colony world that has run afoul (pun intended) of the Hallicheki Hegemony.
The Hallicheki are an avian-like race, ruled by the 'hens', with whom humans have clashed but there now exists a state of nominal peace between the two empires. The rub is that the human colony (founded by a lost colony ship) is firmly within the Hallicheki sphere of influence and the birds want the territory - but they're too smart to do anything that might result in war with the Empire. Instead, they interdict shippijng and make life on the colony world exceedingly unpleasant.
Fortunately, the Hallicheki have their own problems to deal with - a break-away group of worlds (run by the cocks) and it is the presence of these rebellious Hallicheki worlds that GLASS believes will provide the wedge that will allow the Empire to step in.
GLASS, of course, doesn't have any of its own ships or armies, but is instead dependent upon agents provocateur. Irene and her crewmates fit the bill perfectly.
Space Mercenaries is an interesting examination of the laws of privateering, piracy, oceanic shipping and politics transferred from the seas of our world to the deep reaches of outer space. Chandler was a merchant sea captain for much of his life and he took great delight in applying real-world concerns (not to mention the history of sea-faring) to his science fiction adventure tales.
In this novel, he examines and plays with the various laws, customs and regulations that delineate the differences (if there really are any) between pirate and privateer - an exercise that he would repeat later in his John Grimes tale - Star Loot.
He also delves into his Empress Irene character much more deeply than in EoOS; there's quite a number of opportunities for Irena and her husband to clash over divided sexual loyalties (Irene, coming from a human matriarchy isn't too happy that she'll be helping out a male-oriented society of birds break the yolk of their mistresses - but she knows it's the right thing to do.)
Space Mercenaries can be read as a straight adventure tale (one that will pass on a few interesting tidbits of unusual sea faring info), but it is deeper than that; Chandler was one of the few authors writing in the 50s and 60s who dealt seriously with 'equality of the sexes' issues and seemed to play pretty fair with the subject.