We've reached the end of the road, and The 100's penultimate episode just geared us up for an insane series finale. Not to mention, it gave us literally the most painful Season 1 callback we could have ever imagined.

Clarke (Eliza Taylor) and Octavia (Marie Avgeropoulos) spent the episode on a mission to save Madi (Lola Flanery), whom Cadogan (John Pyper-Ferguson) was torturing with M-Cap to find the code that would start the Last War. The girls took the remaining tracker pills to get back to Bardo and then teamed up with Sheidheda (JR Bourne) of all people to rescue Madi.

Unfortunately, they were too late, and by the time they'd found her, Cadogan had gotten the code at a huge price. Madi was conscious and alive, but her brain was damaged beyond repair and she was unable to speak or move, completely locked in her own body. After confirming there was no way to undo or fix the damage, Clarke made the horrifying choice to kill her own daughter and put her out of her misery. 

Octavia offered to be the one to pull the trigger so Clarke wouldn't have to live with one more death, and as she told Madi not to be scared, Clarke hummed a haunting and familiar song to her. 

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Longtime fans of The 100 will recognize this as a callback to Season 1 when Clarke made her very first kill. Years ago, after Atom (Rhys Ward) got caught in the acid fog on Earth, Clarke mercy killed him while humming "All the Pretty Little Horses." There's some pretty morbid irony in mirroring this scene with Madi. Not only did she have another Blake sibling with her, this time, Clarke was the one who couldn't bear to do the deed.

Ultimately, Levitt (Jason Diaz) stopped them before they could actually kill Madi, and then Clarke was off to stop Cadogan from starting the Last War — or taking the Last Test if you believe that alternate theory. It's hard to say whether Madi will survive the finale or whether her fate is sealed at this point. Between her and Emori (Luisa D'Oliveira), who also hovers near death as we head into the series finale, this could be a bloody final chapter for our beloved heroes.

The 100 series finale airs Wednesday, Sept. 30 at 8/7c on The CW.

Lindsey Morgan, <em>The 100</em>Lindsey Morgan, The 100