8 pm/ET FOX
Most people wouldn't willingly enter a tiger cage, unless one takes care of big cats for a living. So when the mutilated body of a doctor is found in one at the zoo after a hospital charity event, Brennan and Booth are reasonably sure the deceased had some help getting there. Adding to the mystery is Cam's disclosure that she was once engaged to the doctor — whose teen daughter she helped raise — so the team ramps up their efforts to find the killer. Chad Lowe guest stars as one of the suspects. —Joe Friedrich

Survivor: Tocantins — The Brazilian Highlands
8 pm/ET CBS
The game nears its halfway point with Days 16, 17 and 18 checked off during tonight's episode, in which the Jalapao and Timbira tribes zero in on which members may be the next targets for elimination. At Jalapao, Taj, who is in control of a secret four-way alliance that crosses tribal lines, comes into the crosshairs of some team members, while at Timbira a few tire of Coach's intimidating ways, which could lead to his early exit. —Tim Holland

CSI: Crime Scene Investigation
9 pm/ET CBS
The landmark series, now in its ninth season, celebrates its 200th episode by bringing in Oscar-winning director William Friedkin (The French Connection; The Exorcist) to scare things up. Most frightening is that one of Ray's former students is murdered. The investigation slams the team into the mysterious world of Mexican wrestling known as lucha libre, in which fighters don masks to conceal their identities. —Tim Holland

9 pm/ET NBC
ER's 15-season run comes to an end tonight with a two-hour episode filled with familiar faces, who return to celebrate the opening of Carter's new medical facility. While closure has been the theme throughout its final season, tonight's last chapter features Gates struggling to save a teen with alcohol poisoning, leaving viewers with the comforting assurance that life at County will go on — even though Thursday nights will never be the same for the show's loyal fans. —Rhoda Charles

Treasure Quest
10 pm/ET Discovery
In March 2007, the Odyssey crew found a wreck dubbed "Black Swan" and its booty, worth an estimated $500 million. Then the Spanish government muscled in on the find and laid claim to the loot. Tonight's first-season finale examines the salvage operation and the brewing legal battle with Spain. Will the crew be able to keep the treasure? Or will this black swan become an ugly duckling for Odyssey's shareholders? —Michael Chant

Free Radio
11 pm/ET VH1
The second season of the improv comedy about a dim-witted radio host opens with Lance going on an ego trip after "Moron in the Morning" wins a local award. The manager responds by hiring an entourage for him. Ed Helms, Dominic Monaghan, Robin Meade and Neil Hamburger are guest stars. —Fred Mitchell