“Damages” (9 p.m., FX) wraps up its great third season with a 90-minute episode. As the action goes forward, we’re told that Patty (Glenn Close) and Tom (Tate Donovan) are on the verge of recovering the money from the Madoff-like Tobin family. But, as we’ve been told from repeated flash-forwards, Tom will end up dead by the end of the scheme.

Just how — and more importantly why — that happens is why we’ve been glued to “Damages” all season. And true to this season’s theme, every major character is either being betrayed by a family member, betraying a family member — or both! Much like “Lost,” this is one series I never want to end.

• Earth Day comes early as ABC celebrates recycling with the “new” sitcom “Romantically Challenged” (8:30 p.m., ABC), which was originally supposed to air last Monday. Alyssa Milano stars as Rebecca, a recently divorced mother who has become rusty about the whole relationship thing.

She claims she hasn’t been out on a date since the Clinton years. That’s funny, since “Challenged” often seems so 1994, a time when “Seinfeld” and “Friends” ruled the airwaves. Rebecca’s sassy sister, Lisa (Kelly Stables), resembles Phoebe from “Friends” reanimated as Karen from “Will & Grace.”

• “American Experience” (8 p.m., PBS, check local listings) presents “Earth Days,” a survey history of the modern environmental movement from the era of post-war consumerism to the Reagan years, with a few nods to the present day. Along the way, we’re reminded of how widely embraced and politically powerful the environmental movement was in the 1970s.

The multiplicity of angles and the torrent of great period footage can be both fascinating and a bit exhausting. A droning soundtrack adds to the soporific atmosphere. But recent history buffs should not miss this. It’s a period that some have done their best to forget, ridicule and erase from popular memory.

• Lisa Ling hosts “Explorer: 25 Years” (8 p.m., National Geographic), a celebration of the show’s first quarter century. It’s the longest-running documentary series in cable history and has been awarded 60 Emmys.

Tonight’s other highlights

• Chuck loses his special skill on “Chuck” (7 p.m., NBC).

• A self-styled “Knight” wastes medieval time on “House” (7 p.m., Fox).

• Jack seeks vengeance on “24” (8 p.m., Fox).

• Rachel Maddow hosts “The McVeigh Tapes: Confessions of an American Terrorist” (8 p.m., MSNBC).

• “Unsung” (8 p.m., TV One) profiles the Bar-Kays.

• Tony discusses food as sensual pleasure on “No Reservations” (9 p.m., Travel).