The Culture and the Idiran Empire are at war in a galaxy-spanning conflict. Horza, a mercenary capable of altering his appearance at will (a Changer), is assigned the task of retrieving a dispossessed Culture Mind by his Idiran handlers. The Mind, while fleeing attacking Idirans who consider its existence an abomination, has taken refuge on Schar's World, a Planet of the Dead. Planets of the Dead are nominally forbidden to both the Culture and the Idirans. On the way to Schar's world he encounters, and joins, a band of mercenaries and pirates, led by Kraiklyn, on their ship, the Clear Air Turbulence. All the while he is doggedly pursued by a Culture Special Circumstances agent, Perosteck Balveda. Kraiklyn unsuccessfully leads the group in a disastrous raid for treasure on a Temple of Light, located on a backward planet, which results in a wildly dangerous gunfight in which some of the crew die. Afterwards, Horza sleeps with and forms an attachment to Yalson, one of the CAT's crew.
On Vavatch Orbital, which is scheduled for destruction in the war, Kraiklyn's Free Company plan to grab a replacement bow laser from an abandoned Megaship, but this also results in catastrophe as the massive ship collides with an iceberg. Horza is separated from most of the crew who escape on the CAT as he escapes on the shuttle with a dying comrade. A sociopathic crew member is left behind and shoots at the escaping shuttle before triggering his nuclear warhead in anger at the crew's abandonment. The damage the radiation caused to the shuttle and its seriously wounded pilot result in the shuttle eventually falling into the ocean. Horza struggles to remain afloat until he is washed onto an island where he encounters The Eaters, a bizarre cannibalistic cult who hold him captive. Horza eventually succeeds in poisoning the leader of the cult with his fingernails and manages to escape in time to watch Kraiklyn play Damage on the capital city of Vavatch, then fights and kills him, to take control of the CAT.
By the time he returns the CAT, he impersonates Kraiklyn's features and fools the crew into believing he is their real captain. Horza is shocked to see Balveda show up in the CAT and he uses his appearance to stun her. Fearing a Special Circumstances plot, he impulsively pilots the CAT out of the GSV in a wild trail of destruction. Balveda reveals Horza's nature to the crew as they watch the Orbital get obliterated by the Culture. Despite Balveda's revelation, the crew decide to follow Horza on his mission. Horza ultimately leads the pirates to Schar's World. There, with the help of Balveda (Horza's enemy who sees it is in her own interests to help him), he fights an infiltration team of Idirans (ignorant of his mission for the Idiran Armed Forces) through its underground railway network in his attempt to capture the prize. In the resulting series of firefights, more of the crew perish. Horza captures Xoxarle, one of the two remaining Idiran soldiers, and believes that the other is dead due to the grievous damage he suffered during one of the battles with Horza's crew. Horza and the pirates underestimate Idiran stamina though, and the presumed-dead Idiran drags his limbless body into one of the trains, driving it on a collision course with the one the crew decide to use to navigate the tunnels. As the collision is about to occur, Xoxarle breaks free and arms himself in an attempt to kill Horza and the crew. The remaining pirates, including Yalson - who earlier revealed she is pregnant with his child - are either killed by Xoxarle or die in the collision. Horza, enraged, pursues the Idiran, but Xoxarle batters him causing his eventual death from cranial trauma. Balveda, who had a multi-purpose Culture device called a memoryform hidden in a false tooth, uses it as a plasma gun and kills the Idiran. Balveda then pilots the CAT along with the Mind back to the Culture.
"Phlebas was an old one too; it was written just after The Wasp Factory, in 1984. I've found that rewriting an old book took much more effort than writing one from scratch, but I had to go back to do right by these things. Now I can go on and start completely new stuff."
There is a debate among Banks fans about which Culture book is the best introduction to the fictional utopia. Consider Phlebas is an obvious contender, being the first published. The Player of Games is sometimes suggested as being easier to read.
Banks said in an interview:
'There's a big war going on in [Consider Phlebas], and various individuals and groups manage to influence its outcome. But even being able to do that doesn't ultimately change things very much. At the book's end, I have a section pointing this out by telling what happened after the war, which was an attempt to pose the question, 'What was it all for?' I guess this approach has to do with my reacting to the cliché of SF's 'lone protagonist.' You know, this idea that a single individual can determine the direction of entire civilizations. It's very, very hard for a lone person to do that. And it sets you thinking what difference, if any, it would have made if Jesus Christ, or Karl Marx or Charles Darwin had never been. We just don't know.'
Gentile or Jew
O you who turn the wheel and look to windward,
Consider Phlebas, who was once handsome and tall as you.