Well, this is definitely a bummer. I thought he was the best part of the show, even if his "knows-everything-about-every-conceivable-topic" was a bit much. (It was based on the U.S. version, who also had a know-it-all detective solving crimes.) 

Still, the one thing you can say about Law & Order is its adaptability. There have been constant cast changes over the years, as you'd expect with a 20+-year-long series. And the show still does well in the ratings. I suppose it's only appropriate that it would happen here, too. But really, after only four years? Even the U.S. turnover was a lot longer than that. 

They will obviously have to write the first character out of the series off camera and explain to viewers what happened to him, although he did go through a bit of an emotional upheaval in the final episode of the season last week, possibly setting up a reason for his departure.

Here's the official announcement from Rogers:

Citytv Orders Fourth Season of Hit Canadian Drama Law & Order Toronto: Criminal Intent and Announces Luke Kirby as New Detective