Keep What You Steal is the 2nd movement of Cortana Suite from the Halo 3: Original Soundtrack. It includes the songs Keep What You Steal and Escape. The first section plays during Cortana rescue cutscene, with the rest during the level Cortana.
It starts with a high strings note, followed by a variation of the piano melody from Finish the Fight. Strings then play the melody of the Gregorian-chant from the Halo Theme. The melody begins to swell, then quiets to a minor key. Strings still take the melody, but drums in the background get louder and louder until they block out the strings. At 2:00, strings begin a discordant melody, which continues to get louder until the end.
The name of the song is derived from Cortana's quote: "I am a thief... but I keep what I steal."
It runs for 2 minutes and 36.133 seconds (2:36.133).