People of Earth

With Sahil not able to locate the Discovery in 3188, Burnham becomes a courier and works with Book, searching for clues about the fate of the Federation. She finds a transmission from Admiral Senna Tal from Earth, but they are unable to travel there with their limited dilithium. After a year, Discovery arrives in the future and Burnham finds them in the glacier. Saru becomes the new captain, and Discoverys dilithium is stored on Book's cloaked ship, which he parks in their docking bay, for safety. Using Discovery's advanced spore drive, they travel to Earth and find it no longer part of the Federation. Investigators from the United Earth Defense Force board Discovery and explain that Tal is dead. They are all attacked by dilithium bandits who the EDF attempt to destroy until Burnham and Book trick the bandits, capturing their leader Wen.

Summary from Wikipedia, CC BY-SA 4.0.