Where can I watch Pretty Little Liars (season 2, episode 1) online for free?
Okay, being a teacher, I need to begin with a plea for you to PLEASE read the actual young adult novel series that the show is based upon! I think you'll find the series is even better than the show!!! (See the link below!)
As for your beloved TV episode, if it's available, you can watch it on youtube. I just typed in Pretty Little Liars Season 2 into their search engine and came up with a huge number of clips already there. I'm sure what you are looking for can be found somewhere on that site. If it's not there now, it may be there tomorrow.
Further, you can also try looking at the ABC Family website. I checked there as well and they have plenty of full episodes right online for you to watch! Often TV websites post the full episode directly after it airs for your convenience.