Ghost Whisperer Episode 4.02 Big Chills

Melinda reconnects with some high school classmates after one of them dies mysteriously. While she didn't really "know" any of them, Melinda "knew of" the cool kids Ryan, Lucas, Haylie and Grace, and was a little surprised when Grace contacted her after she found Lucas dead. Melinda was sure that Grace remembered her from school as the crazy girl who spoke to ghosts, and now Grace was willing to believe a little in order to find out what happened to Lucas. However, while Lucas' ghost remains elusive, another ghost begins haunting Ryan and Grace.

After much sleuthing and a couple of visions, Melinda and Eli discover that Ryan, Lucas and Grace had been involved in a traffic accident where a man had died, but they had covered it up because Lucas, the driver, had been drunk. While they weren't directly responsible for the man's death, Lucas was slowly being driven mad by the secret, and had accidentally overdosed on sleeping pills while trying to get it out of his head. Once dead, he decided to haunt Ryan and Grace as the ghost of the dead man, hoping it would prompt them to come clean.

In the end, Melinda is able to convince Grace and Ryan that its time to fess up, and Lucas is able to cross over.