The Doctor chuckled mirthlessly. "Which part?" he asked, sounding hopeless, and then looked away, pursing his lips together. "Long story short, we're stuck on the an enormous space craft, stuck near the entrance of a black hole. The top of the ship is closer to the black hole than the bottom, so time moves slower on top. Turns out the space craft is from Mondas, and to survive on the bottom of the craft, they begin turning their population into cybermen."
He opened his mouth to continue, but closed it, overcome with grief. Finally, he said, "You were there, Missy... along with Bill and my other companion, Nardole. Bill... " He couldn't say what happened to Bill, so he took a different route. "We ended up closer to the bottom of the ship, and found your previous regneration as the Master was there."
Again, the Doctor paused to grimace. Clearly, this was causing great distress.