The key is that President Martinez catches a glimpse of the VP as the President's going down, which tells him that the VP as responsible. The President in his hospital bed, barely conscious, communicates this to Sterling, who in turn tells the Chief of Staff. But how to prove this? As the Chief of Staff tells Sterling, anything short of absolute proof will mark Sterling as a nutcase.
Time's ticking - with the President sinking, the VP is due to take over as President as per the Cabinet's majority vote. In some of the best sequences of the series, Sterling tries and comes close, but fails to get enough evidence to even present to the Cabinet. They select the VP to serve as President (but nitpick: Sterling as National Security Adviser shouldn't have voted - he's not a member of the Cabinet). Dejected, Sterling at the last minute discovers potential evidence that he had with him all along - the coffee stain, from the poisoned coffee, on his shirt. The President splashed coffee on Sterling when he was falling. (Here's a nice touch to make up for the nitpick: the VP asks Sophia why the poison didn't kill Martinez immediately. She replies it's working as intended, and we later find out out that the poison's being metabolized in the President's body, to leave no trace - which could only happen if he's still alive.)
Meanwhile, Sean and Vicki discover Sophia's secret weapon - after it is en route to the United States. Sean repeatedly asks why Vicki is helping him. She doesn't tell him. A good guess might be that he saved her life, she's attracted to him, some combination of the above. But the identification of the secret weapon gives her a much more powerful motive: the weapon is the deadly Spanish flu, which could well kill Vicki's child if let loose in the U.S.
So The Event is throwing some excellent punches as it ends up this season. Just four episodes left. On the basis of tonight's, I'm hoping there'll be more next season.
See also The Event Debuts on NBC ... The Event 1.2: Aliens! ... The Event 1.4: 24 Back in Action! ... The Event 1.6: Not Only Aliens, Immortals! ... The Event 1.7: The Portal and its Implications ... The Event 1.8: The "Republican" VP and the Anti-24 ... The Event 1.9: "Native Populations, Indigenous People" ... The Event 1.10: Satellite ... The Event 1.11-12: Hardball in Fiction ... The Event 1.13: A Little to Close to the Reality ... The Event 1.14: Upping the Ante ... The Event 1.15: Bluffs and Stakes ... The Event 1.16: High Placed Sleeper ... The Event 1.17: Target Martinez
The Plot to Save Socrates
"a Da Vinci-esque thriller" - New York Daily News
"Sierra Waters is sexy as hell" - curled up with a good book