Case 5 - Dead Rising
First, make your way to the security room to view a short cutscene. Afterwards, wait until 12:00AM (complete some scoops in the interim -- see the Scoops section of this guide for a list of every scoop that occurs on the 21st) and enter the North Plaza.
When the time comes, head into the room near the camera store within the hour. Isabela shows up, but she is being attacked by a zombie. Quickly kill the zombie to trigger another cutscene.
Isabela is injured, so you will have to carry her all the way back to Security Room. A man named Kindell should have spawned in North Plaza at this point. Look just outside the room, and he should be there. He's got a shotgun, so he is a good asset if you want to make it back to the Security Room in one piece.
Look for Kindell in the North Plaza, just outside of the room where you were supposed to meet Isabela.
Put Isabela down for the moment and speak to Kindell a few times. Eventually, the man will agree to follow Frank. To get back to Paradise Plaza, you can either head through Leisure Park, or use the shortcut in Wonderland Plaza. Reaching the Paradise Plaza entrance from the Leisure Park North Plaza entrance while avoiding the convicts isn't too difficult; just hug the northwest wall as you make your way there. Bring Isabela and Kindell to the Security Room to complete the case.