From Halopedia, the Halo wiki
In late September or early October of 2559[Note 1], the UNSC Down Out and Go was ordered by the Office of Naval Intelligence to deliver an encryption key to John-117 behind enemy lines. Due to the need for information compartmentalisation from the Created, as per the Cole Protocol, ONI chose their agent Lieutenant Parisa for the task due to the agent's unique form of memory loss - which caused Parisa to have near-perfect recollection for around seven hours before proceeding to forget nearly everything she'd learnt during that time. To deliver the encryption key, Parisa was to use a shuttle to depart from the prowler, before the Down Out and Go jumped away via slipspace.
List of appearances