Hawaii Five-0's Catherine Rollins has a secret, and it's one that could destroy McRollins on their eve of McGarrett's proposal.

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Fans have waited five seasons for Steve (Alex O'Loughlin) and Catherine (Michelle Borth) to get together, but the latter's yearlong excursion to the Middle East threw a wrench in their long-term relationship. Even though Cath is now back in paradise, it seems her time abroad will continue to cause problems.

A new clip for "Ua 'O'Oloku Ke Anu I Na Mauna (The Chilling Storm Is on the Mountains)" shows that Cath is definitely hiding something. Steve walks in on his girlfriend while she's on the phone, and while viewers can't understand what she's saying, her boyfriend certainly seems concerned (see video here).

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Will McGarrett's proposal plans go awry? Five-0 fans will find out tonight.

"Boiling him down, McGarrett is a warrior with a huge heart," showrunner Peter Lenkov told Entertainment Weekly. "From our first season, Catherine has stolen that heart and now he's ready to take that major leap in their relationship six years later. It's probably one of the bravest things this soldier has ever done."

Catch Hawaii Five-0 Fridays at 9 p.m. ET on CBS.