“Burn Notice” (9 p.m., USA) ends its second season with a cliffhanger centered around an elaborate kidnapping and assassination plot.

For all of the explosions, double-crosses and near-misses, Michael Weston (Jeffrey Donovan) is one cool character. In tonight’s finale, he not only helps out an acquaintance of his old girlfriend Fiona’s (Gabrielle Anwar) new boyfriend, but he also has time to indulge his nagging mother (Sharon Gless) as she indulges his ne’er-do-well brother in a new business venture. And he does this all while posing as an unemployed security guard with a weakness for whiskey.

Weston keeps the audience apprised of his expertise with his voiceover explanations of every technique and maneuver. It’s Espionage For Dummies. “Burn Notice” is smart enough to keep you engaged, fast enough to keep you guessing and just flippant enough to be funny. The inclusion of cult-movie actor Bruce Campbell as Weston’s shaggy sidekick helps, too.

¢ “Seinfeld” took an outlandish idea and pushed it to the limit. If George pretended to be a marine biologist, you knew that a dying whale would show up eventually.

“It’s Always Sunny in Philadelphia” (9 p.m., and 9:30 p.m., FX) is a whole lot louder, dirtier and angrier than “Seinfeld,” but like that show about nothing, it knows how to take a singularly crazy idea to an absurd extreme.

Tonight’s “Sunny” season opener tackles a taboo topic. Enraged that Dee (Kaitlin Olson) and Charlie (Charlie Day) have broken into his stash of frozen meat, Frank (Danny DeVito) convinces them that they have inadvertently devoured a piece of human flesh. Frank’s mind game unfolds with predictable results. At first, Charlie and Dee think he’s bluffing, followed by a period of revulsion, fascination and then an insatiable hunger for the forbidden. Like everything on this show, these stages of cannibalism transpire with the unhinged logic of a profane cartoon. In the second episode, the gang tries to beat the high cost of gasoline only to be implicated in a terrorism plot.

¢ “Blog Cabin” (8 p.m., DIY) welcomes Kevin O’Connor and Roger Cook, talent on loan from the long-running PBS series “This Old House.”

Hosted by Ahmed Hassan, “Blog Cabin” solicits design advice and suggestions from thousands of Internet participants. The entire season shows a Tennessee lakeside cabin being built to their specifications.

¢ A father invests his life savings in a salon only to see his daughters turn it into a social hangout that hemorrhages money. When he is diagnosed with multiple sclerosis, it’s up to the stern British taskmaster to teach the spoiled brats about business – and gratitude – on “Tabitha’s Salon Takeover” (9 p.m., Bravo).

Tonight’s other highlights

¢ On two episodes of “CSI” (CBS), green blood (7 p.m.), death of a sitcom diva (8 p.m.).

¢ “America’s Got Talent” (7 p.m., NBC): the top five.

¢ An eventful night forces Betty into a big decision on “Ugly Betty” (7 p.m., ABC).

¢ The Green Arrow leads the Justice League in search of Clark on the eighth-season premiere of “Smallville” (7 p.m., CW).

¢ Billie takes aim at the list on “My Name is Earl” (7:30 p.m., NBC).

¢ Dean’s stint in the underworld ends on the fourth-season premiere of “Supernatural” (8 p.m., CW).