TORONTO - Although viewers have often been left scratching their heads over the bizarre plot twists on TV's "Lost," the writers have always known how the story would ultimately wrap up, says the show's Canadian co-producer.

"One of the most common questions that we get asked is: 'Are you guys just like, you know, fumbling around the dark or do you actually have a plan?' and the truth is we've always had a plan, always known how the story was going to end up," said Stephen Williams, who divides his time between Toronto and Los Angeles.

"I think the audience needs to be totally and continually reassured that this is not a shaggy dog tale. It's going to wind up somewhere tremendously satisfying and that's always been part of the plan."

"Lost" kicks off its fifth season Wednesday on ABC and CTV in Canada and is set to finish for good in 2010.

And while Williams -- who is also one of the show's directors -- said he's "a huge supporter of the notion of having a finite end to the story" of plane crash survivors on a mysterious island, he'll be sad when the credits roll for the last time.

"I think the worst thing that could happen to 'Lost' is that it would just kind of linger into some sort of pale representation of itself until the ratings dwindled and people's interests dwindled and then finally the show would be killed," he said in a telephone interview from Oahu, Hawaii, where the show is filmed.

"I think it's way better for us to tell the story we wanted to tell, end it on our terms, end it while the story was still a kind of a vital part of the viewers' lives and our lives ... but obviously the disbanding of us all will be a hugely kind of emotionally torturous experience."

This second-to-last season of the Emmy and Golden Globe-winning series, co-starring Canadian Evangeline Lilly, comes eight months after the Season 4 finale in which the island seemingly vanished and the "Oceanic Six" fled on a helicopter.

Williams, of course, couldn't reveal much about the upcoming batch of episodes but did say that "time travel is the new narrative paradigm" in Season 5.

"Lost" has been a huge career investment for Williams, who has directed a slew of other TV series and won a Gemini Award for lensing the Canadian TV movie "Milgaard."

Since he joined the "Lost" team in 2004, he's had to spend nine months of every year filming the series in Hawaii, leaving him with limited time to connect with friends and relatives back home.

"I've been on this show for five years," he said from his office before heading out to scout for filming locations for the 12th episode of Season 5.

"I could only have done that with material that is as rich, and with a cast that is as amazing and a crew and writers that are as singular as the ones that we have on the show. That's the only way that I could've ever stayed invested in a single project for that length of time.

"I think it's been a unique experience for all of us that I doubt we will ever repeat in the spans of our careers."