Stargate Atlantis: Legacy: Allegiance is the third book in the Stargate Atlantis: Legacy series, set after season five of Stargate: Atlantis, written by Melissa Scott and Amy Griswold.
It was preceded by The Lost and followed by The Avengers.
Summary
Still reeling from the shocking discovery that their friend Rodney McKay is now a Wraith called Quicksilver loyally serving Queen Death and with no memory of his true identity, Sheppard and his team return to Atlantis to regroup.
They finds themselves facing a new danger and must face the fact that the unthinkable has happened- one of their own has been turned against them and is now working with the enemy...