New Dirty Harry Ideas

What would be a good idea for a new Dirty Harry movie if Clint Eastwood returned to the role?

Here's my idea:

Harry Callahan is now semi-retired from the police force (maybe he was forced to resign after years of rule-breaking and because the higher-ups thought he was too old) and keeps active by working as a security guard at a local college or high school. He beats up some punk students and teaches them a lesson to show that he is still tough even in old age. Meanwhile, a new killer emerges in San Francisco, and the police bring on Callahan as a consultant to help catch the criminal due to a connection between the killer and a case Callahan solved back in the 1970s (maybe Scorpio if they want to bring the series full circle). Using his wit and classic techniques, Callahan is able to solve the case and catch the killer better than the active-duty police and proves that even in old age he is a badass.