Chuck Season 3 Episode 18 (Chuck s03e18) with title “Chuck Versus the Subway” airs on Monday, May 24th 2010 at 08:00 pm via NBC.
Here is summary for Chuck Season 3 Episode 18 :

In this finale episode, shadowy thugs from the Ring inch closer to take down Chuck and his team, but not if Chuck’s father (Starring by : Scott Bakula) has anything to say about it. Meanwhile, Casey is doing a secret mission to protect his daughter from the Ring

Few hours after original series aired on TV, online streaming video for Chuck Season 3 Episode 18 usually available on Net and of course, if video available, as soon as possible will show you where you can watch this episode for free.