Imrie had only been on the pitch for a couple of minutes when the ball broke to him inside the box and he rifled an unstoppable shot into the roof of the net.
It was no more than Caley Thistle deserved as they came back from a goal down to claim victory.
An early slip by Kevin McBride gave Roy McBain a shooting chance at the edge of the area but he never got hold of the ball properly and the ball drifted tamely wide.
But it took a terrific double save from Robert Olejnik to keep Falkirk level shortly afterwards.
Darren Barr lost his footing and Adam Rooney pounced but Olejnik guessed right to get a hand to the ball and then was alert enough to block Garry Wood's follow-up effort.
Neither defence looked particularly convincing in the early stages and Mark Stewart was allowed to run at the Caley Thistle defence but his low shot was comfortably dealt with by Michael Fraser.
John Stewart nodded inches wide from a Scott Arfield cross with Fraser relieved to see the ball slip past his right-hand post.
Graham Barrett then just failed to get on the end of a cutback from John Stewart as Falkirk looked set to make the breakthrough.
Mark Stewart almost fashioned an opening for himself when he chased down Fraser and the goalkeeper's clearance struck his boot but the ball bounced harmlessly away.
Barr was caught in possession again after 27 minutes when Rooney hounded him and raced in on Olejnik but the goalkeeper again came to his captain's rescue.
Falkirk made a meal to trying to clear it and Rooney had another opportunity but this time he sent his effort high and wide.
Don Cowie went closer with a measured effort from the angle of the penalty area which Olejnik seemed to get his fingertips to but referee Mike McCurry awarded a goal-kick.
It was Falkirk that edged in front after an hour. Barrett cut the ball back and Mark Stewart was quick to cash in as he slid the ball in at the far post.
But Cowie equalised eight minutes later with a low 15-yard shot after Falkirk had failed to clear Iain Vigurs' corner.
Worse was to follow for Falkirk as a mistake by Barr led to confusion in their own area and, after Cowie's shot had been blocked, Imrie followed up to slam the ball high into the net.