Plot hole: After Meaghan's best friend was shot why wasn't the bullet matched to confirm the shooter? No way would she have not heard a gunshot 10 feet away in the bathroom of her apartment even with towel around it. No rookie would be given a temporary detective badge after a shooting.
Character mistake: Why would the rich witness be at the supermarket himself and using a taxi cab?
Factual error: There is absolutely no way a rookie patrolman could become a detective overnight. Total fiction.
Other mistake: When Meghan Turner is riding on patrol with her partner, her first night on the job, her partner tells her to pull over to go inside a mini mart so he can take a leak. The time frame he was in the restroom, from the time she stopped a robbery, does not add up. Unless her partner was in the restroom emptying his bowels or reading a magazine, he should have come out of the restroom quickly to join his partner to foil a robbery. He was gone over 20-something minutes to take a leak?
Other mistake: NYPD probably has several thousand detectives throughout all five of its boroughs. I seriously doubt that Nick would have been the lead detective on a murder accusation involving Megan. NYC precincts employ several hundred officers, so the chances of him working a murder case involving her would be slim to none unless the murder took place within his precinct's jurisdiction.