First responders should watch their backs; Hawaii Five-0's latest villain is targeting Oahu's bravest in three new sneak peeks for "Lehu a Lehu."

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Remember season 5's murderous arsonist, Jason Duclair (Randy Couture)? Well, he has a fan, and his secret admirer will do anything to get his hero out of prison. After taking out a bomb squad, the latest pyro will threaten the island with a swath of hidden bombs if Duclair isn't released from prison.

With their backs against the wall, McGarrett (A;ex O'Loughlin) and Danny (Scott Caan) head to Halawa to see if Couture's character can identify the man behind the some creepy fan poetry. Donning a straight jacket, the prisoner will be less than cooperative (see first video below).

'Hawaii Five-0' Season 6: 'Really Fun' Hurdle Coming For McDanno, EP Teases Trouble

Meanwhile, McGarrett will put his own spin on planning his proposal. The soldier's Navy SEAL side will shine through as he attempts to put together a romantic evening (see third video below).

"I've been planning the op," McGarrett assures a skeptical Danno. "I secured a ring. I reconed a location. Now I've just got to execute."

Find out how well that goes when Hawaii Five-0 airs Fridays at 9 p.m. ET on CBS.