Every officers worst nightmare comes true for Malloy & Reed while on patrol: Another officer radios in for 'officer needs help', but then doesn't respond when asked for their location. Since there wasn't a call-sign associated with the call for help, no one knows who needs help.
The dispatcher then follows procedures and starts a division wide radio "roll-call" in order to account for every officer on patrol. While the roll-call is going on, calls for service from the public still needs to be handled. When a motorcycle officer fails to check in when prompted, a division wide search is instituted to look for him, which Malloy & Reed are assigned to assist in.
While driving in a residential area, Reed believes may have spotted a down police-cycle in the entrance to an underground parking garage. As they get closer, they are able to see that it is in fact a police cycle on its side. They then radio in their location, then exit their vehicle to enter the parking garage cautiously, not knowing what they will find.
Inside the garage, they discover the missing officer is ok, but involved in an armed hostage situation. With two additional officers on the scene, the police are now able to free the hostage from the gunman.
However, the motor officer has plenty of explaining to do with Sgt. McDonald, in that he failed to follow proper procedure to insure the dispatcher had his location & call-sign before engaging the gunman.