‘NCIS: Hawai’i’: Swift Reveals Major Threat in Series Finale Part 1 Sneak Peek (VIDEO)

At the end of the last episode of NCIS: Hawai’i, Sam (LL COOL J) learned, after he had Ernie (Jason Antoon) get into a laptop the Elite team found in one of The Chemist’s labs, that the entire operation was compromised. There was a Trojan horse that was activated the moment anyone tried to break into the internal files, and it infected whatever system tried to access it—and the Elite team was the first to do so. Whoever planted it had been in the Elite server for three days.

Now, in the two-part series finale—CBS has canceled Hawai’i after three seasons—it’s time to figure out who’s responsible, and this case brings Agent John Swift (Henry Ian Cusick), as we previously reported, back to the island. TV Insider has an exclusive sneak peek of him filling Jane (Vanessa Lachey) in on the case in the April 29 episode.

They’re dealing with “a biological weapon, unlike any we’ve ever seen,” says Swift. “Untraceable, airborne, nearly incurable. … He was the last chance to stop it.” He’s referring to The Chemist, who was killed (as revealed in the promo). Everything has been bagged and tagged, Sam confirms, and it’s all on the way back to Pearl, along with the witnesses .. though one person is missing. Watch the full video above for more about this person.

The two-part series finale kicks off on April 29 with “Spill the Tea,” in which a high-value bioweapons expert is murdered in a secure facility on Hawai’i, and NCIS and the NCIS Elite team join forces to track down the killer and discover an even deadlier threat. Then, in the second part on May 6, “Divided We Conquer,” following a devastating ambush with a deadly bioweapon, the NCIS team must track down a mysterious terrorist group before they can strike again.

“There is definitely a special twist that comes in towards the end. It was a shock to me when I was reading the scripts, that’s for sure,” Alex Tarrant (who plays Kai) told us. And yes, the finale “most definitely … ends on a cliffhanger.”

How do you think the series will end? Let us know in the comments section, below.

NCIS: Hawai’i, Mondays, 10/9c, CBS