Steadfast (The Lost Fleet: Beyond the Frontier #4)

DEFENDING THE ALLIANCE. The search for two missing lieutenants leads Admiral Geary and the crew of Dauntless on a far-flung chase, ultimately ending at the one spot in space from which all humans have been banned: the moon Europa. Any ship that lands there must stay or be destroyed—leaving Geary to face the most profound moral dilemma of his life. As strains on the Alliance grow, Geary is ordered to take a small force to the border of Syndic space. But what he finds there is a danger much greater than anyone expected: a shrewd and powerful enemy that could finally force the Alliance to its knees.

Praise for Jack Campbell's The Lost Fleet series:
“Once again, the visceral action comes fast and furious... Well up to the high standards established by this intriguing series.” Kirkus Reviews

“One of the best military science fiction series on the market.” Monsters and Critics