The Skirmish on Mona Lisa was a minor conflict that occurred in the debris field of Installation 04 in the Soell system aboard the prison ship Mona Lisa between UNSC forces and an outbreak of the Flood on October 25th, 2552. The Mona Lisa was sent to the area as an ONI secret project to study the effects of the Flood on humans and Covenant species, and to determine its effectiveness as a weapon. When contact was lost with the Mona Lisa, the UNSC Red Horse was sent to investigate. Upon investigation, the Flood was found to have completely infected the ship, and the Mona Lisa was destroyed. All Marines sent to the Mona Lisa were killed, along with the Flood infection.