“4,722 Hours” is episode five of season three of Marvel’s Agents of S.H.I.E.L.D.
This episode opens with the events at the end of the season two finale, “S.O.S.: Part 2”, when Simmons was sucked into the Monolith. At the end of the previous episode, “Devils You Know”, Simmons had decided to tell Fitz just what happened in the six months she was missing. Now, this is her story, and it’s all shown as events from that time, with occasional hours listed (up to 4,722).
Simmons was taken to an alien world with a breathable atmosphere, yet the world seems dead. There’s also no sun, and it seems to be in endless darkness (that should make it too cold to live on, but there is an explanation given).
She isn’t alone on the world, there’s someone else there, the last survivor of a years-old NASA expedition. There’s also something else there, that is apparently responsible for the deaths of the other members of the expedition. How NASA came to have the Monolith isn’t said. The survivor is the reason Simmons wants to go back there, to see if he’s still alive, as he wasn’t able to get through the portal, and rescue him.
This episode is totally about Simmons. Other than her and her fellow survivor, only Fitz appears in it, and only at the very end.