On tonight's NCIS: Los Angeles, an ex-Marine is suspected of creating a chemical bomb, prompting the special ops team to join the FBI’s domestic terrorist task force and leading to the typical inter-agency struggles.

There's already conflict in the scene shown below, in which the team's theory on what happened doesn't mesh with their counterparts' view. But the bureau may be mistaken, according to a familiar face.

Find out who it is - as well as which NCIS special agent is the eternal optimist who's into musicals (take a guess) in this sneak preview clip from the 20th episode of the season, "Patriot Acts" ...

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