While many credit or blame “Survivor” for the reality-TV era, the real grandaddy of the genre has got to be “Cops.” Its use of cheap and grainy documentary footage offers a sense of realism, and its subject allows viewers to enter the shabby back alleys of neighborhoods both alluring and forbidding. And like the best and most popular shows, “Cops” offers a blend of the shocking and the expected. The action on “Cops” is always different and always the same.

Two decades later, the new series “DEA” (10 p.m., Spike) expands and refines the “Cops” formula. The series follows a squad of agents for the Drug Enforcement Agency as they investigate, entrap and arrest drug dealers in some of the nastiest neighborhoods of Detroit.

At first, the atmosphere is all macho attitude and paramilitary regalia. It soon settles down to high jinks and banter between guys whose daily routine mixes boredom and adrenaline in a nine-to-one ratio.

For all of its bluster, “DEA” operates on a level of ambiguity that is both refreshingly honest and deeply unsatisfying, at least from an entertainment perspective. The agents get almost all of their information from confidential informants. That’s a fancy name for snitches, or rats, or busted dealers who agree to offer evidence and even pretend to buy drugs as evidence in order to get a lighter sentence or no sentence at all.

In tonight’s pilot, the agents make bust after bust, and after each arrest, they offer their prey lenience or complete absolution if they cooperate and help them find bigger dealers. After an elaborate stakeout and bust, they tell a heroin dealer that they “can make this all go away” if she leads them to Mr. Big. Or at least Mr. Bigger-than-she-is.

This shows a great deal of independence and latitude offered the DEA agents and a deviation from the typical cops-and-robbers plot. People watch cop shows, and most dramas, for a story with a beginning, a middle and an end. That’s why both “Cops” and “Law & Order” have been popular for 20 years. “DEA” presents a tale without resolution on a treadmill of futility in a world of moral twilight.

¢ The two-part series “Return to the Amazon” (8 p.m., PBS, check local listings, concludes next week) follows oceanographer Jean-Michel Cousteau and his team as they return to a rain-forest base first explored by Jean-Michel and his famous father, Jacques Cousteau.

Filled with eye-popping photography of the river and rain forest, “Return” celebrates the remarkable biological diversity of the area while raising awareness of its rapid ruin. In the 25 years since Cousteau visited, an area the size of Texas has been deforested.

Tonight’s other highlights

¢ A repeat two-hour “Mythbusters” (7 p.m., Discovery) takes on pirate lore.

¢ The documentary “Autism Every Day” (7 p.m., Sundance) follows eight families coping with the disorder over a 24-hour period.

¢ A contestant’s swan song is sung on “American Idol” (8 p.m., Fox). Every departing contestant will appear on “The Tonight Show” on Wednesday until a winner emerges.

¢ Last night, Barbara Walters talked about people living to 150. The special “Caring for Your Parents” (8 p.m., PBS, check local listings) looks at how families are scrambling to look after elderly parents who are living decades longer than before.