Shonda Rhimes has already explained that the two-hour episode will involve a multi-car pileup and a fire in a female doctor's home.
Rhimes has now told Entertainment Weekly that the finale will be split between "sanctuary" and "choices".
"The theme of the first hour is sanctuary, which sort of uses the idea that the hospital is our characters' safest place and our safest place as viewers," she said. "[Then we use] the hour to slowly turn that on its head [so] that by the end, the hospital is definitely kind of the least safe place in the world."
She continued: "The second hour is about choices, and we get to watch our characters make big ones. Lexie [Chyler Leigh] chooses between Mark [Eric Dane] and Alex [Justin Chambers]. Owen [Kevin McKidd] chooses between Teddy [Kim Raver] and Cristina [Sandra Oh].
"Bailey [Chandra Wilson] faces the hardest medical choice that a doctor has to make. And the other choice that's being made is Callie [Sara Ramirez] and Arizona [Jessica Capshaw] and whether or not they're going to be together or not. It is going to come down to the baby thing."
The season finale of Grey's Anatomy will air on May 20 on ABC.
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