Osiris — Speak with Osiris

"Guardian, I'm glad that you're here," Osiris says. "The Cabal continue to run rampant through the timelines of Mercury. The temporal instabilities they've caused are in danger of infecting the rest of the system."

He shakes his head. "We can't allow the corruption to spread. We must repair more of the obelisks. You will find them in the EDZ and on Nessus. Reactivating them is the only way to ensure the effects of the Sundial are contained."