"NCIS" is celebrating a milestone very few television series have reached: 300 episodes.

Details of the episode, titled "Scope," have been kept understandably quiet ahead of Tuesday's premiere, but series star Mark Harmon has promised the outing will not disappoint.

"We have certain episodes that make the hair on the back of your neck stand up when you close that last page. This is one of those," he told Contact Music. "It's a case-driven episode, a story that drives this team to do what they do best."

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We do at least know that the episode will feature guest star Taye Diggs as a Marine suffering from PTSD who factors into the teams investigation.

"For our 300th episode, we needed a guest actor who could proudly portray one of our nation's wounded warriors as well as participate in a very touching musical performance,"executive producer Gary Glasberg said in a statement. "This emotionally charged role is tailor-made for Taye Diggs, and we are so thrilled and honored to have him join us."