The Sundial, Fields of Glass, Mercury

Osiris: I told you before - I tried to save Saint-14. I bent the rules of time using a prototype of the Sundial. It allowed me to walk the corridors of time here on Mercury. But I failed. I never found Saint's final moment against the Vex. I encountered younger versions from his first mission to Mercury, among others. But none were the right Saint. The prototype Sundial still exists, accessible off the main deck. And it can still travel through Saint's personal timeline on this planet. But venture there at your own peril. He cannot be saved. I have walked every permutation of those corridors with a hundred thousand of my Echoes and found nothing. Saint-14 is lost.