Once your wristwatch is close to midnight, head over to the North Plaza and enter the unfinished store seen with a question mark above. The store is not far from the fountain, and Kindell Johnson will likely be just outside. (That's the store front seen above.) Talk to Kindell and he'll join you.
Enter the store to trigger the opening cutscene. Isabela is late - and is under attack from a zombie when she arrives.
Take out the zombie with your weapon of choice. A shotgun blast did the job just fine for me.
Killing the zombie triggers another cutscene.
Find a Nail Gun here before exiting the store.
Clear a path ahead of Isabela and Kindell. Set a waypoint on the door to Leisure Park and carry Isabela there.
Hug the left wall to avoid as many zombies as possible. While carrying Isabela, you are untouchable as long as you keep running.
Set a waypoint on the Paradise Plaza doors and pace back and forth with Isabela on your back as you wait for Kindell to get close enough to zone with you.
Carry Isabela to the warehouse door and clear the area of zombies. Set the door as a waypoint then clear a path for Kindell.
You don't actually have to enter the air shaft, just get close and this cutscene initiates.
You'll receive 50,000 PP for rescuing Kindell.
Case 5 is now complete. Case 6 starts at 3:00am, which for me is just a few minutes away.
Once 3:00am hits, be in the security office to trigger this cutscene. Isabela explains the mysteries behind the zombies...
...and Doctor Barnaby becomes a zombie.
This lengthy cutscene comprises Case 6 in its entirety.