Marauder

From the front flap Tor UK first edition: "Megan has a mission. But must she sacrifice herself to save our worlds? Pilot Megan Jacinth has three goals, all seemingly unattainable. She has to find her friend Bash, who she left for dead to save her own life. Then she must use Bash's unique skills to locate an ancient space-faring entity - the Wanderer. Lastly she needs to save human-occupied worlds from an alien incursion, using the entity's secrets. The odds seem impossible, but the threat is terrifyingly real. Megan finds Bash, but the person she'd known and loved is a husk of his former self. Bash is also being held captive by Gregor Tarrant, her greatest enemy. Tarrant needs the Wanderer too - even more than he needs Megan dead. However, his motives are far more sinister. And he's near to finding Megan's most closely guarded secret. A race across space to reach the Wanderer seems Megan's only option. But this entity, also known as the Marauder, is far from benign. The price for its knowledge may be just too high. Megan should know, as she still bears the scars from their last encounter..."