Klara and the Sun meets S. A. Barnes's Dead Silence with a touch of Becky Chambers' A Psalm for the Wild-Built in Nebula Award-finalist A.D. Sui's darkly philosophical murder mystery, as a death monk and a team of researchers trapped onboard a spaceship of the dead encounter something beyond human understanding....

Vessel Iris has devoted himself to the Starlit Order, performing funeral rites for the dead across the galaxy, guiding souls back into the Infinite Light. Despite the comfort he wants to believe he brings to the dead, his relationships with his fellow Vessels are distant at best, leaving him reliant on his AI implant for companionship.

The spaceship Counsel of Nicaea has been lost for more than a thousand years. A relic of Earth's dying past, humanity took the ship to the stars on a multi-generation journey to find another habitable planet yet never reached its destination. Its sudden appearance has attracted a team of academics eager to investigate its archeological history. And Iris has been assigned to bring peace to the crew's long departed souls.

Carpeted in moss and intertwined with vines, Nicaea is more forest than ship. Skeletons are all that remain of the crew, and Iris' religious rituals are met with bemusement by the scientists—and outright hostility by the engineer Yan Fukui. Determined to be more than just the curator of the dead, Iris tries to make himself useful to the team, desperate to form friendships.

But Nicaea's plant life isn't the only sentience to have survived in the past millennia. Something onboard is stalking the explorers one by one. And Iris with his AI enhancement may be their only hope for survival....