They are A'tuu'shahn'i, the Rim's mercenaries of choice, ancient, enigmatic shape-shifters rumored to be organic machines, possibly from a different dimension altogether. Invincible, implacable, unstoppable-except to an even more ancient, equally implacable enemy from within. For the crew of the patrol ship Baidarka, finding A'tuu'shahn'i warriors on a routine rescue mission is a disaster. Having to work with them is even worse, especially as both human and A'tuu'shahn'i are only waiting for the betrayal they are certain will come too soon.