NCIS could be welcoming back its biggest star. Insiders say Mark Harmon is seriously considering a return to the long-running series after ratings slipped to No. 10, a sharp drop for a show that once reigned as the most-watched drama on television. “People are nervous, and it feels like a bad omen,” a source reveals. “Now there’s talk of Mark coming back on at least a recurring basis – maybe even full-time – to turn things around.” Harmon, 73, played Special Agent Leroy Jethro Gibbs for 18 seasons before leaving early in season 19. While he’s stayed on as executive producer, he has largely kept a low profile. Recently, though, he’s reemerged as executive producer and narrator of NCIS: Origins, which follows a younger Gibbs, played by Austin Stowell. His behind-the-scenes involvement has fueled speculation that a bigger on-screen comeback is next. Not everyone, however, is thrilled. Some insiders complain Harmon has already been “throwing his weight around” as an executive producer and fear he’ll interfere with their work. But the actor isn’t letting that stop him. “Mark doesn’t care who he ruffles,” says a source. “If ratings are sinking, he feels he has every right to come back, steady the ship, and help NCIS reign again. Otherwise, the show could go down the drain.” Fans may recall Harmon’s brief cameo connection through Origins, which teased the possibility of more appearances. Now, with NCIS itself in crisis mode, Harmon appears ready to step out of semi-retirement and make his presence felt once again. “If anyone can save this show,” the source adds, “it’s Mark.”