Gibbs (Mark Harmon) and the "NCIS" team are in a race against time on tonight's episode when a terrorist group threatens to detonate a "dirty bomb" in Washington, D.C. -- and ET's Kevin Frazier is on the set.

Of course, Gibbs is working with a handicap. On last week's show, he pushed McGee (Sean Murray) out of the way of a speeding car and was thrown over the hood, injuring his shoulder. Now he is in a sling and McGee is trying to do penance.

"He feels a little responsible," Sean tells ET. "He feels he owes him a little bit and maybe he is going to be his caretaker and Gibbs may not like having a caretaker, but McGee is going to try to be a caretaker no matter what."

Gibbs is a bit amused at McGee's efforts to act as a nursemaid, but he doesn't find it a bit funny when he reencounters attorney Margaret Allison Hart (Rena Sofer), who has once again insinuated herself into his investigation.

"The payoff for that is a returning character [Sofer] that has been introduced earlier in the year has some surprises, too, because that relationship started in a certain place and, like most things on this show, it develops with a different angle," Mark tells Kevin.

There is also a bit of comedy tonight when McGee wears a tuxedo to the office for an Internet wedding that is taking place in Spain. And Sean says he knew the minute he read the script that the writer had attended at least one. Turns out it was two.

"The man in the wedding is one of our [post-production] producers. He gave up a wedding video for this online wedding," says Sean, who also admits that despite playing a computer expert on the series, he doesn't have a clue how to put together an Internet wedding. "The technology of putting together an online wedding, that's technology far superior than anything I can begin to dream of," he admits.

The "Masquerade" episode of "NCIS" airs tonight at 8 p.m. on CBS.