Alex McKenna and Death is Not the Beginning

In the fourth and final installment for the series, Alex faces his most difficult case yet: the school bully.
For two years, Kyle had no qualms making Alex's life even more complicated than it already was.
Choosing to single him out for his psychic abilities, the angry teen took every chance to undermine Alex's well-being. But When Kyle is unexpectedly murdered, his ghost seeks out Alex for the very power he'd been stigmatized for.
Despite their fraught history, Alex must set aside old wounds to help a soul in need. Searching for the killer, Alex uncovers why Kyle had victimized him so intensely, and it's not what he ever could have expected. The truth, it turns out, will set them both free.

The Alex McKenna Series in order:
Alex McKenna and the Geranium Deaths
Alex McKenna and the Academy of Souls
Alex McKenna and a Winter's Night
Alex McKenna and Death is Not the Beginning