Last Stand (Star Legions: The Ten Thousand Book 4). Star Legions: The Ten Thousand, #4

The Black Legion has vanquished every army and fleet sent against it, yet now this invincible Legion is in full retreat as it races away from the Emperor's wrath. They gambled all on a single decisive battle, and with it lost everything. With victory against the Emperor now impossible, the Legion finds itself lacking purpose and money. They came to the Empire with promises of glory and reward, but now they are trapped and surrounded on all sides by enemies.
The massacre of the Legion's officer corps leaves it vulnerable, and it falls to warriors like Xenophon to hold back their desire for revenge and to put them on a path home. The God King Artaxerxes is no fool, and he knows he cannot let a massive Terran fleet make its way through his domain unchallenged. To do so would encourage dissent in his already weakened empire. He may have fought off his brother, Lord Cyrus, but the threat of revolt is ever near.
Mobilising forces from every corner of the Empire, he throws them all at the Legion under the command of his trusted lieutenant Tissaphernes. Last Stand is the fourth book in the Star Legions series from Michael G. Thomas, the bestselling author of the Star Crusades series. Previously published as the Black Legion series.