AMBULANCE SHIP begins with "The Secret History of Sector General" - White's introduction discussing the series to date - then proceeds to the 3 linked short stories of this volume, introducing Sector General's special ambulance ship Rhabwar (named for a famous figure in Tralthan medicine, being Tralthan-built).
Some misconceptions might arise for new readers (or even fans of the series who haven't previously encountered this book). Rhabwar isn't special just because it's an ambulance ship; those are actually common in White's universe already. What's special is that somebody in the Galactic Federation government has applied some lessons learned from Sector General's previous adventures. (Points to the author for giving an interstellar civilization credit for some common sense.) Someone has noticed that over the last 20 years, the Monitor Corps has found 3 new civilizations while Sector General has found 7 - since distress calls are much easier to find than any other communication signal. Once contact has been made, the hospital's track record for establishing friendly relations is also much more impressive than the Corps' - since saving lives makes a MUCH stronger impression than ordinary diplomacy.
Until the opening of this story, the Federation hasn't had a set policy for dealing with mysterious distress calls - on the face of it, why would they, until it became obvious that they needed one? Calls that DIDN'T happen to fall within Sector General's area have usually resulted in the death of any unknown aliens involved, since regular ambulance ships are specialized for various known species (usually only one or two). Rhabwar, therefore, has been specially built to handle all kinds of atmospheres, shapes, and sizes on its casualty deck, and is kept in reserve for distress calls that don't correspond to any known flight plan. (As a bonus, of course, it can fill in for just about any known species' ambulance craft, if needed.)
Senior Physician Conway, his wife pathologist Murchison, and the fragile Cinrusskin empath Prilicla (with their considerable experience of ship rescue operations and first contacts) have been assigned to Rhabwar. White also introduces Naydrad, the caterpillar-like Kelgian heavy rescue specialist, as part of the new Rhabwar team.
"Contagion" - As a shakedown assignment for Rhabwar, the team has been assigned to an ordinary search-and-rescue job: responding to a distress call from the Earth-human-crewed scoutship Tenelphi. This job begins as an opportunity for White to introduce the ship and Captain Fletcher as he and the medical team begin feeling out their relationship (which continues throughout the book). After all, what could go wrong with a simple chore like rescuing the Tenelphi?
"Quarantine" - After the Tenelphi job, Rhabwar's first proper assignment - answering an unknown distress signal - cropped up soon afterward: responding to a distress signal from a ship torn apart by hyperdrive failure. One survivor was found: a child of the previously unknown species.
"Recovery" - O'Mara orders the medical team and crew of Rhabwar to spend their on-duty time aboard ship until they've established routine procedures. (The crew's training in rescue procedures by the medical team and the reciprocal training in ship procedures didn't get launched properly in all the excitement, so White smoothly provides the usual overview of species classification for those who came into the series late.) Their next rescue job introduces the two species later known as the Blind Ones and the Protectors of the Unborn.
RELEVANT NOTE: Compared to the Protectors of the Unborn, the Blind Ones have little exposure in the Sector General books. However, White didn't waste the idea; see FEDERATION WORLD.
IRRELEVANT NOTE: The Dean Ellis cover art on the 1st US edition purports to show Rhabwar approaching a very large derelict spacecraft, but in narrative reality, the ship doesn't just carry a simple red cross - it also bears the equivalent symbols from cultures across the Galactic Federation.