Castle playfully asks the question: What would have happened if the recent late-night wars resulted in murder?Nathan Fillion ) appears to promote his latest novel on a talk show hosted by Bobby Mann (guest star Tom Bergeron), Mann tells Castle that somebody wants him put him off the air permanently. "He turns to him as they're signing off and asks for his help because he feels like he's been marked for death," Bergeron tells TVGuide.com. "And clearly he's right."Bergeron, who already pulls double duty hosting ABC's Dancing with the Stars and America's Funniest Home Videos, jokes that ABC is becoming the "All Bergeron Channel." But he did enjoy acting — even as a corpse.Bill Bellamy plays the host of the show that follows Mann's (and who's eager to take Mann's time slot); Dan Cortese is the network executive who tells Bobby he needs to make some changes to his format; and Fred Willard portrays Mann's sidekick of 35 years — who perhaps is tired of laughing at Mann's lame jokes.Willard, who played sidekick to Martin Mull's character in the '70s talk-show send-up Fernwood 2-Night, says he looked to Ed McMahon when getting into the role.Stana Katic). "You see hundreds of these shows where someone is being grilled by these detectives. It's like a parlor game," he says. "And I've never played anything like that on TV, so it was kind of a challenge. The question was: How do I answer these without appearing too innocent or too guilty?"Castle airs Monday at 10/9c on ABC.