Melissa McKay

First Lieutenant Melissa McKay was a UNSC Marine and ODST. In 2552, she was stationed aboard the cruiser Pillar of Autumn and led a company of some 130 ODST soldiers aboard the ship. Her commanding officer was Major Antonio Silva, and her platoon commanders were Second Lieutenant Dalu and Second Lieutenant Oros. However, Dalu was later reassigned as supply officer, and his job was taken by Master Sergeant Lister.

When the vessel fled The Battle of Reach, she was wounded in action by Covenant boarding parties. Nonetheless, she made the jump from the Pillar of Autumn to the surface of Installation 04 aboard a Human Entry Vehicle. She was third in command of the survivors of the Autumn, under Major Silva and Captain Keyes. and helped secure the Pillar of Autumn's crash site. After leading the attack to capture the mesa that would become Alpha Base, she met the Master Chief for the first time. Major Silva was very antagonistic toward the Chief, but McKay was one of few ODSTs to actually look up to the Chief. She figured that it was a matter that Major Silva, and men in general, would not understand.

She led a convoy of Warthogs and Scorpions from the crash site of the Autumn. On the way back to the base, they encountered resistance from Covenant forces under field master Noga 'Putumee. Nevertheless, she managed to ferry a large number of supplies from the ship to the base.

She went on a patrol the next day and picked up Yayap. Later she was in Alpha Base when Zuka 'Zamamee attempted to infiltrate the base to find the Chief. She then took the remains of Pelican Charlie 217 and set them up as though the ship had crashed so that the Covenant would come and the humans could ambush them. The Covenant came, but so did the Flood. McKay was horrified at the first sight of the Flood, nevertheless, she managed to capture one Combat Form alive, the form of the former PFC Wallace A. Jenkins. She then interrogated him and compiled the first tactical information on the Flood.

Later, using Jenkins' information, she helped to prevent an attack on the base by the Flood long enough to evacuate it.

She then asisted in the attack on the Covenant-held Truth and Reconciliation, having guards drag Private Jenkins along for the ride.

After the vessel's capture, McKay realized that Silva was planning on taking the vessel to Earth so that he could become the hero of the people. She realized that this was not only in violation of the Cole Protocol, but that if a single Flood Carrier Form made it to Earth, all of humanity could fall to the Flood. Most of the vessel had not yet been sterilized from the Flood when Silva ordered it to take off.

McKay disobeyed Major Silva's direct orders and severed the Truth and Reconciliation's fiber-optics connection to the reactors to keep the Flood from escaping the Halo. Her actions cost her, and a few hundred marines and Naval personnel their lives, but it stopped the Flood from killing thousands, if not millions, of innocent people throughout the galaxy.