“GOSSIP GIRL” — (8:00-9:00 p.m. ET)“Con Heir” (TV-14, DS) (HDTV)DESMOND HARRINGTON RETURNS AS JACK BASS / BILLY BALDWIN GUEST STARS — Chuck (Ed Westwick) invites Jack (Harrington) to town to thank him for saving his life, but finds the trip doesn’t go exactly as planned. Blair (Leighton Meester) and Dan (Penn Badgley) attempt to consummate their new relationship — but unexpected roadblocks get in their way. Meanwhile, Ivy (Kaylee DeFer) finds an unlikely ally in William (Baldwin) in her quest to be accepted on the Upper East Side, and Nate (Chace Crawford) is hopeful a new investor will save his newspaper. Blake Lively, Kelly Rutherford and Matthew Settle also star. Joe Lazarov directed the episode written by Annemarie Navar-Gill.