The Spheres of Heaven2001

"Set about 20 years later in Chan Dalton's career than the events of The Mind Pool (1993), this hard-science adventure finds humanity still quarantined by the nonhuman sapients of the Stellar Authority for having killed other intelligent life-forms. But a Stellar Authority ship is missing in the distant Geyser Swirl, and humans are the best candidates for finding and rescuing it. Under retired General Dag Korin's command, Dalton tracks down most of his old colleagues and sets off in a recycled warship. Meanwhile, a human expedition is already deep in the swirl, on a planet it has named Limbo. By the time Dalton's company arrives, nearly everyone on Limbo needs to be rescued from the militaristic Malacostracans, who have occupied it because of its strategic location at the nexus of links to many alternative universes. The yarn's tight plotting, economical but vivid characterization, and abundance of ideas argue that Sheffield continues to be an authentic sf master."--Booklist.