It's not easy being Carrie Mathison, that's for sure.

In this tense, suspenseful episode of 'Homeland,' we finally learn the truth about her mystery ailment: she's bi-polar, and has been since college. Deprived of her medication following the attack on the square, which sent her to the hospital with a concussion and some nasty facial abrasions, she cascades into full-scale mania, berating the staff of the hospital over its inadequate supply of magic markers (my favorite line of the episode: "Is green elusive? I mean, my kingdom for a fucking green pen!") and giving Saul an awful scare. When he questions her, Carrie admits that her sister is medicating her, and Saul and Maggie Mathison are soon splitting up chaperone duties like a pair of amiable ex-spouses, since it's obvious that Carrie can't be left alone while she's in this condition.

Alarmed as he is by Carrie's predicament, Saul does not make the mistake of discounting what she has to say. Right away, he sees the wisdom in her frantic declaration that Nazir would never pin all of his hopes on a single sniper, even one whose target is the president himself. Saul relays the warning to Estes, who mentions it to Vice President Walden, who is waiting out the scare in an undisclosed underground bunker. Walden swats away this unhelpful suggestion -- "You want your portrait up at Langley some day? Focus on that. Find Walker. And fire somebody. I don't care who." -- and also discloses a vital piece of information: he's running for president, and plans to announce his candidacy next week.