NCIS: Los Angeles' Marty Deeks would like to requisition one set of lead-lined boxers, thanks you very much.

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Gunnery sergeant Hugh Patterson will pop up on the OSPs radar when he comes down with a case of radiation poisoning, and Deeks (Eric Christian Olsen) will be concerned for his little swimmers when he heads undercover in "Core Values."

The LAPD detective wants a Geiger counter in the midseason premiere sneak peek, but Hetty (Linda Hunt) has a better idea. Whatever the case, Deeks wants to ensure his future as a father.

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"I've got my lineage to think about, you know?" Deeks says. "It could be the end of the Deeks family tree."

According to Sam (LL Cool J), that would be doing the world a big favor.

Geiger counters and lead-lined underwear aside, Kensi (Daniela Ruah) and Deeks will quickly find themselves undercover when they find out the victim had been moonlighting as a security guard for a defunct nuclear power plant. Their mission won't be smooth sailing, either. There's a least one explosion looming in their future.

Find out more when NCIS: LA returns to CBS on Jan. 4 at 10 p.m. ET.