On Scorpion Season 2 Episode 24, Team Scorpion realizes that Toby is missing. When they learn that Mark Collins escaped, it becomes clear what happened. Now, it's a race to find Toby, and for Sly, it's a struggle to keep Happy from finding out the proposal secret. Happy can sniff out a lie, and Sly isn't the best at keeping secrets.
While in the hospital, Mark has been working on BBI aka Brain to Brain Interface. When he saw that Megan died, Mark figured that Walter must have worked on a brain trust for her. Mark wants Walter's research because it will help with his own.
But is that really what Mark wants?
Team Scorpion starts to get suspicious. When Walter realizes that Mark isn't actually torturing Toby, Team Scorpion starts to wonder. Tim points out that this makes Mark unpredictable. We don't know what he's truly after.
Meanwhile, Mark decides to be a life ruiner by ruining the proposal surprise. Toby does use it to his advantage though. He convinces Mark to allow him a phone call to say goodbye to Happy, and during that phone call, Toby tells Sylvester where he is. Okay, the birds in the background do that for Toby, but that was actually the whole reason Toby called.
Mark's endgame was to challenge Team Scorpion. He makes Walter face the fact that Team Scorpion has made him weak because Walter runs off to save Toby instead of ensuring that Mark is captured.
In the end, Mark is captured. Toby is saved. Toby proposes to Happy who reveals she is married to another woman, and Walter realizes he loves Paige who he just sent off on a romantic weekend with another man. How's that for a finale?