MONTREAL — Cinar Films of Montreal has pacted with Nickelodeon to co-produce 20 episodes of teen whodunit series “The Mystery Files of Shelby Woo,” which will begin shooting this spring in Montreal. Nickelodeon already has produced 20 half-hours, which have been airing Sunday nights on the cable web.

The U.S. network decided to shoot the new batch of episodes on film rather than video, and the increased budget led it to seek out a co-production partner. Cinar seemed a natural choice, given that the Canadian kids TV producer has a long history with Nickelodeon, having produced the animated series “The Busy World of Richard Scarry” and the live-action show “Are You Afraid of the Dark?” for the web.

“We’ve had a relationship with Cinar in the past,” said Marjorie Cohn, vice president/executive producer of current series at Nickelodeon. “They produced the first of our big Nickelodeon hits, ‘Are You Afraid of the Dark?’ “The agreement gives Cinar international rights to the series and Cinar execs are optimistic that it will be a strong seller. “Part of the fun of the series is that viewers get to play along,” said Patricia Lavoie, VP of live-action production at Cinar.

Series, aimed at the 9-12 demographic, stars Irene Ng (“The Joy Luck Club”) as a teenage detective who has an after-school job as an intern at the local police department. Veteran thesp Pat Morita (“The Karate Kid”) plays Shelby’s grandfather, Mike Woo, who is a retired criminologist. The series was created by Alan Goodman.