Master Chief 117 awoke inside the control room of Halo; a Forerunner installation set up to destroy whole galactic civilizations (effectively killing the Flood's food; starving it), where he watched 343 Guilty Spark and Sergeant Johnson talking as he was inserting Cortana into the central terminal in order to light the ring.

"Oh, hello!" The Monitor cheerily greeted, floating next to the Sergeant's face. "I've been running through some early simulations; no promises, but the installation should be ready to fire in just a few more days!" He said.

"Tch! We don't have a few more days!" Johnson replied, now standing at the terminal. The Chief turned and aimed at the door. If any Flood came in, they would enjoy a meeting with his MA6B Assault Rifle.

"Bu-bu-But a preliminary firing will DESTROY the Ark!" Spark argued in panic; he loved the installations architecture, and the humans were going to wipe it away needlessly?
"Get over it." Johnson sighed as he began to put Cortana into the console.

"You'll destroy this installation...?" Spark said in a dark, deeper tone, as his optical unit turned red, this would, in Forerunner terms, signify that the AI has gone rampant and the machine has turned against it's makers.

A large blast of red plasma hit Johnson in the face, it was so hot that it melted some of the skin off of his body, but Johnson managed to silence the scream as he fell to the floor. The Master Chief turned.

"Unacceptable, Unacceptable! Protocol dictates action, I see now that helping you was wrong!" Spark shouted as he sped through the air at the Master Chief, he looked the SPARTAN in the eye.

"You are a descendant of my makers, inheritor of all they left behind...but this ring...is mine." He said menacingly, his eye glowing red in the darkness. This darkness enveloped the room, the last thing that the Master Chief saw was that glowing red eye in his face as he returned to consciousness.

"Chief! Chief? Oh thank God..." Cortana sighed as she saw the Spartan get up slowly, shaking off the aching of his muscles. He was still on the ship and so was Cortana, but there was something different...It was overtaken by Flood, and rotten flesh covered the walls, reminiscent of how High Charity, the Covenant holy city, had looked when Master Chief had set foot in it when it landed on Earth.

He reached out and took Cortana's chip, inserting it into his neural network through the neural port at the back of his head. He had the usual feeling of slight vertigo, and mercury, which soon subsided.

"What happened?" The Chief asked. 
"We've landed on the planet that the Gravemind has pulled us into." She said.

"Looks like our only choice now is to find out why he wanted us here." He replied, reloading his assault rifle. "Hm. Gravity seems normal." He added as he finished. "How's the air here?" He asked.
"Scanning-" Cortana quickly replied. "Hm...Seems like we're in a sustainable atmosphere. You can breathe this air without particular trouble."

"Strange." Master Chief said as he finished loading. "Let's go." He said as he walked out of the ship. Once he jumped out of one of the holes tore into it, he found that he landed on a solid surface.