Plot summary
Bakshi accidentally reveals to Morse that Whitehall is actually Reinhardt, a Nazi scientist who was working on the Obelisk before being captured by the SSR and imprisoned for life by Carter in 1945. In 1989, Reinhardt was released from prison by Alexander Pierce to find that a woman he had found in 1945 was still the same age. Dissecting her, Reinhardt discovered the secret to her immortality and used it to make himself 44 years younger. "The Doctor" finds the remains of the woman, who was his wife, and vows vengeance against Whitehall, with whom he is now pretending to be allied.
Grant Ward also appears to join in an alliance with Whitehall, after having tortured Christian into confessing past sins and then apparently murdering him and their parents. S.H.I.E.L.D. hacks a United States Air Force mapping satellite and uses it to find the hidden city. Coulson meets "The Doctor", who knows that the Obelisk (or the Diviner) is a key that must be taken to the city by someone it deems to be worthy.
Credits
Adapted from Wikipedia contributors, Agents of S.H.I.E.L.D. season 2. HTML formatting and reference markers removed.