“Stargate Atlantis” (8 p.m., Sci Fi) enters its second-to-last hour with a tale of a vicious killer run amok in America’s gambling Mecca. The slogan “What happens in Vegas, stays in Vegas,” never seemed more apt.

After a series of unsolved brutal murders that leave their victim a desiccated husk, Detective John Sheppard (Joe Flanigan) is at his wits’ end. Those wits get twisted further after he’s taken to Area 51, where he gets a tutorial in the real source of the killings — a renegade Wraith who crash-landed on Earth and who has since gone on a killing spree (for energy) while plying the poker tables of Las Vegas to earn the money to concoct a device capable of phoning home to the Pegasus Galaxy, a toll call with ominous implications for the planet.

For casual fans of the show and of sci-fi in general, the hour’s highlight has to be moment when the Wraith, disguised as a deranged punk biker, insinuates himself into a mobster’s poker game, featuring “Sopranos” stars Steve Schirripa and Frank Vincent. Filled with menace and dry humor, the scene makes you wonder if there is a future in a “Mafia vs. the Aliens” movie genre.

• For the second year running, the Miss America pageant becomes a reality elimination series on “Countdown to the Crown” (9 p.m., TLC). Contestants from 50 states and territories have embarked on the Queen Mary ocean liner, where they face a series of challenges over four one-hour episodes. Viewers at home should pay close attention, since they have the power to vote four worthies into the final round.

• Viewers can spend the day with “I Love Lucy” (7 a.m. to 8 p.m., Hallmark). The marathon celebrates the debut of the sitcom on Hallmark. “Lucy” debuted in 1951 and has never gone out of style. To put that in some perspective, when “Lucy” first aired, Truman was president, Stalin ruled the Kremlin and the Korean War raged. Americans were still driving Packards, Studebakers and Hudsons across America’s 48 states without the benefit of an interstate-highway system. Elvis Presley was just another teenager dancing to songs by Patti Page, Perry Como and Rosemary Clooney. All of that seems like ancient history now, but the world still loves “Lucy.”

Tonight’s other highlights

• Utah and Alabama clash in the Sugar Bowl (7:15 p.m., Fox).

• The 1999 prequel “Star Wars Episode I: The Phantom Menace” (7 p.m., Spike) examines Anakin Skywalker’s formative years.

• Catch seven episodes of “Extreme Loggers” (7 p.m. through 2 a.m., Discovery).

• Victory plans a major move on “Lipstick Jungle” (8 p.m., NBC).

• A federal agent goes astray on “Numb3rs” (9 p.m., CBS).

• Scheduled on “Dateline” (9 p.m., NBC): With her husband accused of the unthinkable, a wife teaches herself forensics and challenges a police investigation.

• Scheduled on “20/20” (9 p.m., ABC): odd and extreme parenting stories, including serial surrogates, nursing 8-year-olds and “fake” babies.

Cult choice

A fresh-faced young man (Kyle MacLachlan) follows a victimized chanteuse (Isabella Rossellini) to the dark side of a sleepy lumber town in director David Lynch’s audaciously lurid 1986 melodrama “Blue Velvet” (6:25 p.m., IFC).