A converted freighter, the Mona Lisa was a prison ship taken over by ONI Section III to perform experiments on Flood specimens found among the debris of Alpha Halo, using both human and Sangheili prisoners as test subjects.

In October 2552, the prowler UNSC Red Horse was sent to investigate the Mona Lisa after contact was lost. Deploying Marines to the prison ship, much of the squad was lost to the Flood, and the prowler destroyed the Mona Lisa with a nuclear missile.

High above Threshold, this gas mine is similar to the facility occupied by Sesa 'Refumee's faction. Scans of the gas mine were collected by the UNSC Red Horse during its survey of the Soell system following the Battle of Alpha Halo.

Simply known as "Henry," this Sangheili was a prisoner of war held aboard the prison ship Mona Lisa to be studied by ONI. When they began to test Flood specimens on the prisoners, ONI personnel quickly lost control of the ship.

Henry saved a human prisoner from an infected guard and they hid until Marines from the UNSC Red Horse found them. With the prison ship's destruction imminent, Henry and Sgt. Lopez fought over the last remaining escape pod. It is unknown if he survived.