Let the countdown begin. Last year’s most exciting and innovative drama, “24” (8 p.m.), is back. And from the looks of the first two episodes, it’s just as good as ever. The action picks up a year after last season’s conclusion. Sen. Palmer (Dennis Haysbert) has won his election and is now in the White House. The fate of his weird and controlling wife is not entirely clear. Jack Bauer (Kiefer Sutherland) is still recovering from the death of his wife (Leslie Hope), who was killed by his former lover Nina (Sarah Clarke). Nina’s fate and location also go unmentioned.

Not unlike former Vice President Al Gore, Bauer has taken a year off to feel sorry for himself, grow a beard and gain some weight. He’s first seen wearing a ratty old plaid shirt and avoiding phone calls from his old colleagues at the Counter Terrorist Unit. He also tries to visit his daughter Kim (Elisha Cuthbert), who has taken a job as an au pair for a combustible Hollywood couple. Kim avoids Jack because he reminds her of her mother and his role in her murder.

But there isn’t much time for family dynamics. Jack gets back to work only after President Palmer informs him of a terrorist threat to blow up Los Angeles and personally requests his return to the terrorist unit. And as you might expect, Jack has only 24 hours to save the day. And just like last year, Kim gets in trouble just when the fate of the nation requires her father’s undivided attention.

Viewers who miss an episode of “24” can catch repeats at 10 p.m. on the following Monday and 4 p.m. the following Tuesday on the FX network.

“NOVA” (7 p.m., PBS) expands to two hours to present “Galileo’s Battle for the Heavens,” a dramatic re-creation of the epic confrontation between the Renaissance scientist and the Roman Catholic Church. British actor Simon Callow (“Four Weddings and a Funeral”) portrays Galileo in dramatic re-enactments from a scientific career that changed our perception of the universe.

Tonight’s other highlights

Kitty makes a big announcement and receives a visit from her parents (Betty White and Tom Poston) on back-to-back episodes of “That ’70s Show” (7 p.m. and 7:30 p.m., Fox).

Two siblings bicker over a crucial bone marrow donation on “The Guardian” (8 p.m., CBS).

British racecar driver Jeremy Clarkson hosts “Speed: Without Limits” (8 p.m., TLC), a look at the effects of speed on the human body.

Amy guards her family against her stalker on “Judging Amy” (9 p.m., CBS).

Scheduled on “Dateline” (9 p.m., NBC): Passengers and crew on a crippled 747 recall their harrowing ordeal.

Clark fears that his dad may have become a snitch on “NYPD Blue” (9 p.m., ABC).

Scheduled on “Real Sports with Bryant Gumbel” (9 p.m., HBO): an interview with a gay NFL veteran.

Series notes

A pilot sues a female officer for sexual harassment on “JAG” (7 p.m., CBS) … A model (Brooke Burns) thinks Finch is a woman on “Just Shoot Me” (7 p.m., NBC) … The kids have outgrown Paul’s Halloween dreams on “8 Simple Rules” (7 p.m., ABC) … Lorelai hosts an Elizabethan feast on “Gilmore Girls” (7 p.m., WB).

Halloween decoration wars on “The In-Laws” (7:30 p.m., NBC) … Cheryl personal space on “According to Jim” (7:30 p.m., ABC).

More tricks than treats on “Frasier” (8 p.m., NBC) … Trick or treating, Chicago style, on “Life with Bonnie” (8 p.m., ABC) … Frank awakens in a compromising position on “Haunted” (8 p.m., UPN) … Clark meets his grandfather on “Smallville” (8 p.m., WB).

Doug deludes himself on “Hidden Hills” (8:30 p.m., NBC) … Claude fears being replaced by a temp on “Less Than Perfect” (8:30 p.m., ABC).