Defender is the eleventh book in he Kris Longknife Series. After Kris meets Rita Nuu-Longknife, she transports great-grandmother and a delegation of Alwans to the system where the old Wasp had engaged the Alien mother ship. While Kris and her party are examining the hulk, three Alien vessels come through a jump and attack Wasp, which destroys all three.

Wasp returns to Alwa. Kris and Jack Montoya take some time to get to know each other better (physically). Their vacation is interrupted when Navy vessels jump into the system in strength, bringing with them King Raymond I. Ray promotes Kris to full commander and immediately frocks her as a commodore. He then appoints her as his viceroy for the Alwan Sector.

Jack and Kris marry.

Kris tests the responsiveness of the vessels in her command and has to relieve one of the ship's captains, Carolyn Sampson. After getting logistical processes started at Alwa, Kris searches for and finds Phil Taussig and the surviving crew of USS Hornet. An alien vessel jumps into the system; Kris engages and disables the alien, captures the hulk and returns it to the Alwan system.

Abby Nightengale and Steven Bruce formalize their relationship and set up housekeeping.

More Royal United Society Navy vessels jump into the Alwan system and Kris learns that she has been promoted to captain and frocked as a rear admiral. Vessels from the Helvitican and Musashi navies jump in. Kris organizes her command and its logistics tail just in time for the arrival of an Alien mother ship in the Alwan system.

Kris's command defeats and destroys the Alien forces, suffering some losses itself. During the Battle of Alwa, there was evidence that observers from other, unknown, Aliens nations were present. The observers escaped through a jump point during the battle.

Penelope Lien returns from her reconnaissance mission to report that she believes she found the home world of the Aliens. The remnants are as primitive society and a large pyramid-shaped structure.