River of bones

the long version

Commander Matt Reddy and his crew are afraid it may finally be the end of the USS Walker. Ever since their ship was transported to another world, and they became embroiled in a deadly conflict between the Lemurians and the vicious Grik, the Walker has been taking a pounding. With Walker out of commission for repairs, Reddy takes command of a different ship and joins a desperate battle to block the Grik swarm. Meanwhile, the humans and their allies face a deadly second front in the Republic to the south.