The knockout rounds begin on The Voice (7 p.m., NBC/Ch. 5), but as per network policy, we don't know which contestants will perform tonight.The format is that each of the coaches picks two singers at a time from his/her team, and each of them performs a song of their own choosing. After both have performed, their coach selects a winner and that person advances to the next round of the competition.There are 32 singers remaining, so we'll just have to tune in to see if BYU grads Ryan Innes and/or Amy Whitcomb are on tonight's episode.Elsewhere on TV ...How I Met Your Mother (7 p.m., CBS/Ch. 2): The gang tries to put together a legendary bachelor party for Barney.Dancing with the Stars (7 p.m., ABC/Ch. 4): The remaining contestants perform.Bones (7 p.m., Fox/Ch. 13): A string of murders is tied to FBI agents. (Season finale)Defiance (7 and 9 p.m., Syfy): Insects are unleashed on the town.Rules of Engagement (7:30 p.m., CBS/Ch. 2): Timmy quits.The Following (8 p.m., Fox/Ch. 13): Ryan tries to stop Joe Carroll. (Season finale)90210 (8 p.m., CW/Ch. 30): Jordan ends things with Naomi.Warehouse 13 (8 and 10 p.m., Syfy): Pete and Myka race to stop a plague.Mike & Molly (8:30 p.m., CBS/Ch. 2): Mike and Molly try roller skating.Hawaii Five-0 (9 p.m., CBS/Ch. 2): A film crew follows the Five-0 team at an inopportune time.Castle (9 p.m., ABC/Ch. 4): Beckett steps on a pressure-sensitive bomb.Revolution (9 p.m., NBC/Ch. 5): Aaron goes with Rachel to the Tower.The Secret Life of the American Teenager (9 p.m., ABC Family): Ben tells Amy she should break up with Ricky.Bates Motel (11 p.m., A&E): The motel opens for business.