Operation: ATHENA was a covert UNSC mission to infiltrate the Song of Retribution, and retrieve the Janus Key from Jul 'Mdama and his Covenant remnant forces in September 2558. The mission participants consisted of Spartan-IVs Sarah Palmer, Gabriel Thorne, and Holly Tanaka, who used Sangheili spy Ayit 'Sevi to smuggle the Spartans aboard Jul 'Mdama's ship prior to his fleet travelling to the Forerunner Absolute Record and use the Janus Key to find the location of all Forerunner artifacts. A battle ensued between UNSC, Covenant, and Forerunner forces under control of the Absolute Record's protector, the Custodian. While quizzing the UNSC and Covenant forces of their intent, the Custodian determined no one was worthy of wielding the Absolute Record, and the ancilla destroyed the Janus Key. Jul, some of his remaining forces, and the Spartans all managed to escape, but access to the Absolute Record was lost.
These events are depicted in the comic Halo: Escalation Issues #20-24.