The red convertible Winifred Hill was driving has the same license number (WPA 384) as a green hardtop seen several weeks earlier.
When Mannix arrives at the Holiday House he parks next to a red VW which is parked next to a blue Chrysler convertible fitting the description of Clay Riegles' car. After Mannix and Winifred Hill are shot at, Mannix pursues the shooter. The next scene shows an empty parking spot next to the red VW. Mannix does not appear to recognize that the blue Chrysler is gone and does not tell the police either. This is done solely so Mannix can be the hero and save the day.