Frederick Weller and Mary McCormack, In Plain Sight

It took until the very last day of shooting on In Plain Sight, but after five seasons and 61 episodes, the show finally brought them together for good.

"We had two people on our production team get engaged a few hours before we wrapped," Frederick Weller tells TVGuide.com.

"Mary [McCormack] set the whole thing up. She pretended like she just wanted to make a speech between takes. She asked if anybody else had anything to say. The second A.D. stood up and said he just was so happy to be able to work on the show for five years with the woman he loves — they've been with us since Season 1 — and then he pulled out a ring. It was pretty intense."

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Will the same fate hold true on-screen for the USA crime drama's will-they-or-won't-they couple, Mary and Marshall? On Friday's series finale (10/9c on USA), Mary is on Marshall's mind as his nuptials to Abigail (Rachel Boston) near. "Marshall's fighting with Abigail at the beginning of the episode," Weller says. "Marshall is in a state of even greater confusion than the average soon-to-be groom...because of his relationship with Mary."

The death of Mary's fugitive father (Stephen Lang) will lead to a conversation five years in the making. "Marshall's efforts to help Mary psychologically and spiritually with the death of her father will be dovetailed into his need to discuss their intimacy and their relationship," he says. "This is the big talk that Marshall and Mary have needed to have since Season 1."

Exclusive In Plain Sight sneak peek: Can Mary ever forgive her fugitive father?

Although Weller is tightlipped about whether this talk will lead to Mary and Marshall finally getting together, he says he believes fans will be satisfied with the last episode. "I think that the script was terrific," Weller says. "It's going to be one of our best episodes."

After five years, Weller thinks the timing couldn't be better for Mary and Marshall's little chat — as well as for the series to wrap up with a shortened eight-episode season. "I love the job, but it was time to stop teasing the audience about Mary's father and about Mary and Marshall," he says. "In fact, 12 episodes this season might have been too long. I feel like once those tensions are concluded, after that, it would never really quite be the same show."

The timing may be right, but the end still hasn't completely set in for Weller. "It's very strange," he says. "I wanted to get together with Mary to watch the last episode, but we're going to be out of town." It's this close relationship with his on-screen partner-in-crime-solving that Weller will miss the most. "We'll still hang out," he says of McCormack, "but acting with someone is a specific kind of communication. It's that dynamic, that interaction that I'll miss."

In Plain Sight's Mary McCormack: "It feels right" to end the series now

Looking ahead, Weller, who recently moved to Los Angeles, has his sights set on doing more studio films. "The films I've done are all pretty small — the films that I wasn't cut out of," he says with a laugh.

However, he doesn't rule out a return to the small screen. "I would love to do another series if I like the character. That was the wonderful thing about this job," he says. "I had stability, but I also felt artistically fulfilled because I enjoyed the character and the people I was working with."

The In Plain Sight series finale airs Friday at 10/9c on USA.