Reid Scott Replaces Jeffrey Donovan in Law & Order Season 23

Donovan's character, Detective Frank Cosgrove, written off due to being 'too honest', paving the way for Scott's Detective Vincent Riley.

Jeffrey Donovan, who played Detective Frank Cosgrove in seasons 21 and 22 of Law & Order, has been written off the show and replaced by Reid Scott as Detective Vincent Riley in the season 23 premiere.
Donovan's departure was explained in the show as Cosgrove getting 'jammed up' for being too honest about things people aren't too honest about these days.
Reid Scott's character, Detective Vincent Riley, was introduced as a new series regular, filling the void left by Donovan's departure.
Scott's character is paired up with Mehcad Brooks' character, Detective Jalen Shaw, in the new season.
Donovan reportedly left the show due to creative differences.