Sean Murray has been on NCIS since its 2003 premiere - and the writers are still surprising him with Special Agent Timothy McGee's story lines. The actor, 48, exclusively told Us Weekly that the Tuesday, November 18, episode is "something that we've never quite done yet," and it's all about McGee and his Deep Six books. "McGee is back at it again with his Deep Six novels, doing his thing, writing his book, and he has a little bit of a run-in with an obsessed fan and McGee gets kidnapped," Murray teased. "He's in a little bit of trouble, and he's got to figure his way out of it." In order to crack the case and get out alive, McGee has to turn to the fictional Deep Six characters for help. Did You Catch the OG Vera's Return on 'NCIS' and 'Origins' Crossover? McGee's book characters are based on his NCIS team in Washington, D.C., but with a few big differences - which make for a comedic hour of TV. "It was great. It was a challenging episode for us, for sure, because [when] we get together, we know each other shorthand as our agents, as our characters," Murray explained, noting that seeing Gary Cole as Professor Parkman is proof he's a "chameleon." (Cole usually plays Alden Parker.) The actor teased, "It was fun to see Gary come in and do this fully realized kind of English professor character. Somewhat Ducky, like, a little bit," referring to the late David McCollum's portrayal of NCIS medical examiner Dr. Donald "Ducky" Mallard, who was British. Sean Murray. Bill Inoshita/CBS Murray revealed that Katrina Law, who plays Jessica Knight, had an equally fun role as the fictional Agent Knightshade. "She's in a sort of Tomb Raider, superhero outfit sort of thing. I mean, all that was fun," he shared. "I remember the first time we all got together, Katrina is going, 'Should I try an English accent? Should I do, like, a kind of a cheesy English accent? What level should we [have]?'" Murray hinted that her accent as Knightshade is over the top because they had "fun with it." 'NCIS' Universe Dating History: 'NCIS: Sydney' Stars' Love Lives, More Wilmer Valderrama, explored two totally different vibes between Nick Torres and his book persona, Rick Soares. Torres is known for being rough around the edges, a badass agent and loyal to a fault. His alter ego, however, is nerdy, scared to ruffle feathers and much more reserved. "Seeing Wilmer come in and figure out Rick Soares was one of my favorite things in the world," Murray told Us. "The sweater vest, the glasses, the intonation in his voice. All of it is so good." Are Any 'NCIS' Characters Mentioned in 1st 'NCIS: Tony and Ziva' Episodes? The make-believe portion of the episode isn't just for Murray's counterparts, as he also gets to play McGee's alter ego, McGregor. "I think that McGee would like to be a little bit cooler, a little bit more proactive [like McGregor]," Murray said. "But I think all of us have that version of ourselves that we're looking for." When it comes to the case itself, Murray told Us, "You hope things are going to work out OK," teasing the conclusion unfolds in a "pretty respectable way." NCIS airs on CBS Tuesdays at 8 p.m. ET.