So here's where we're at in the game. I've been running prelude to Hunter as if it is actual story. So the outcome is basically set. Two of the PC's are/were related, and the motivation is that the sister/wife (and child) were killed by something supernatural.
The culprit is a fairly powerful Strix, who'd been riding around in the Mother's body.
"She" had been gruesomely killing people, and straight up said she killed the daughter after she was taken into custody. The mother is now dead, the Coroner says she probably died of throwing herself into walls after she'd been institutionalized. The Coroner's assistant suggested, privately, she'd been dead for 2 days even though she'd been talking to them hours earlier. update a few more hints that were given, a patient released was singing her favorite song, obnoxiously at the same time they were leaving the hospital, around the time "she would have died" (OOC Joke "time is on my side" from movie fallen. Other pieces got avoided by character choices or dice rolls (the cops beat the players to finding the wife, and then the husband chose to have her instantly commited to an institution and didn't talk to her long).
A piece of my problem is that our supernatural specialist left the game, she was not happy, and no one else was really happy with her role play/participation. That generally left the party with a bunch of bruisers, who now have been only mildly respeced to have some more occult/investigation.
How should I go about ensuring the players continue to pursue this?
The problem, as I see it, is that it does fly in the face of reason that they should continue to pursue it. It's almost like metagaming to pursue it. Though I'm not sure suggesting a bit of metagaming is bad in this case (we are wrapping up a prelude after all). I personally feel a bit like saying, I know it doesn't make sense in the real world to pursue anything, but the thing about hunters is that they contiue to pursue in even when the most obvious solution (wife went nuts) would answer the question.