A rogue fleet assembled by the disgraced former cadet Nick Locarno, who persuaded junior crews on ships of many powers to mutiny and join him behind a Trynar shield in the Detrion system.
Nova Fleet is the threat behind the fourth season of Lower Decks. Across the season an unidentified vessel appears to destroy Klingon, Romulan, Orion, Ferengi and other ships. In The Inner Fight and Old Friends, New Planets it emerges that the ships were not destroyed but taken, their lower ranks having been talked into overthrowing their officers.
The instigator is Nick Locarno, expelled from Starfleet Academy after the Nova Squadron accident. He abducts Beckett Mariner, expecting her to share his resentment of authority, and proclaims an alliance answerable to no government, secured by a black-market Genesis Device.
Mariner steals the device, and the captured crews soon quarrel among themselves. The Cerritos breaks through the shield using the Orion battleship won by D'Vana Tendi's bargain with her sister, and Locarno is caught in the Genesis detonation.