Before the mass murderering ghost kills people, he marks them with a number. Frank can see the numbers so he knows who the next victim will be and does his best to protect them. This lands him in hot water with the police and he is viewed as a suspect. Frank is then on the run from the police, while trying to save the marked individuals.
This movie is listed as a comedy-horror but it's only a little bit funny and not that scary. But hey, it's Michael J. Fox's last live-action movie before going into semi-retirement.