"You heard the lady. Locate the Prophet, take him down."
Regret is the ninth level from Halo 2. The previous level was Delta Halo and next level is Sacred Icon. The mission is about John 117 having to find the High Prophet of Regret in the Surface of Installation 05 and kill him in order to prevent Halo from being activated.
Make your way through the set of Towers
Ride the Gondola to the far Towers
Pass through the submerged Structures
Reach the main Temple
Kill the Prophet of Regret and escape
When the Covenant Fleet jumps in, the audio the jumps make travel at many times the speed of sound. There should be a delay.