08/09/2012 08:27 pm ET

'Falling Skies' Preview: Terry O'Quinn Guest Stars As Noah Wyle's Mysterious Mentor (VIDEO)

Whenever a show is in need of a charismatic (but vaguely threatening) authority figure, we imagine Terry O'Quinn is first on a casting director's speed dial.

In the penultimate episode of "Falling Skies" Season 2 (airing Sun., Aug. 12, 9 p.m. ET on TNT), O'Quinn guest stars as Arthur Manchester, a former history professor and mentor to Noah Wyle's Tom Mason.

In our exclusive clip from this Sunday's episode, we see Tom and Arthur reunite in Charleston, S.C., where the 2nd Mass has retreated in the hope of finding safety. Naturally, O'Quinn's character is in charge, acting as the President of the New United States in all but name -- but is he as benevolent as he seems?

We'll get another full episode of his character to find out -- O'Quinn will also guest star in the sci-fi drama's season finale, airing August 19.

Watch our exclusive sneak peek, above, and tell us: Do you trust Arthur?

2012 Renewal Index: Canceled, Safe and on the Bubble Shows