TONIGHT'S MUST-SEE

"Heroes," 8 p.m., NBC. You rarely hear people say: "Save the cheerleader, save the world." When they do it on this compelling show, however, it somehow makes sense. The cheerleader (Hayden Panettiere) is indestructible, but doesn't know why. Tonight, she hopes to get answers from her birth parents. Others around the country have their own powers and problems.

OF NOTE

"How I Met Your Mother," 7 p.m., CBS. A night of comedy reruns begins here. Ted returns to the annual Halloween party where he once met the perfect woman before losing her phone number.

"The Class," 7:30 p.m., CBS. If you haven't been watching this show yet, start with this hilarious rerun. A hurricane is bashing the area. Holly, the status-conscious reporter, is soon being pelted on live TV. Kat is soaked and angrier than usual; she wants to goad a confrontation between the too-pleasant Ethan and his former fiance.

"American Experience: The Great Fever," 9 p.m., PBS. In 1900, Dr. Jesse Lazear had a radical theory that yellow fever was spread by mosquito bites. He put himself at risk, was deliberately bit by an infected mosquito, proved his point — and died in two weeks. This documentary studies the efforts to wipe out a disease that killed 20,000 Americans during an 1878 epidemic.

"Friday Night Lights," 9 p.m., NBC. Last week, we saw the intense buildup to an arch-rivalry football game. Now game time nears amid desperation. "Voodoo" Tatom, the transfer quarterback, clashes with teammates and with the coach — who sees his job crumbling.

"What About Brian," 9 p.m., ABC. Remember when most of the characters here were kind of happy? Now Marjorie has left, Adam and Brian are trying to get over her, Dave has been thrown out by his wife and the company is in trouble.