Chris O'Donnell and Mark Harmon Chris O'Donnell and Mark Harmon

CBS has issued its official press release and first photos for the two-part NCIS episode that will serve as a backdoor pilot for a spinoff starring Chris O'Donnell and LL Cool J.

Titled "Legend," the episode kicks off April 28 and concludes May 5. In one of the photos, Mark Harmon's Gibbs is seen walking-and-talking with O'Donnell's Special Agent G. Callen.

The setup: When the discovery of a Marine's corpse becomes a matter of national security, Gibbs' team must collaborate with — AOA! Acronym Overload Alert! — the NCIS' OSP, aka the Office of Special Projects.

Joining O'Donnell and LL Cool J at the OSP are Louise Lombard, Daniela Ruah and Peter Cambor, who plays an operational psychologist.

One final tease from the Eye: "Meanwhile, Tony snoops into Ziva's personal life." Yeah, I thought you'd like that.

Though "Legend" is the title of the NCIS episode, the spinoff, should it be picked up as a series, is as-of-yet untitled.

Crave TV scoop? E-mail senior editors Matt, Mickey and Tim at