Video previews: http://abcnews.go.com/2020

ON A TWO HOUR "20/20," TONIGHT, FRIDAY, JULY 27

On tonight's two-hour "20/20" on ABC (9:00-11:00 p.m., ET):

9:00 - 10:00 p.m.:

"20/20" reports on a real-life online murder mystery. A chance encounter in an online chat room leads to romance between a beautiful 18-year old girl and a handsome young marine. But what she doesn't know is that her "sweet sexy marine" is actually a 46-year old married man. And before it's over, passion will turn to jealousy, a love triangle� and murder.?? "20/20" investigates a mystery where nothing is what it seems. Jim Avila reports. (OAD: 3/19/10)?

10:00 - 11:00 p.m.:

Can the grief of losing a child be to blame for the uncharacteristic and shocking actions of a once prominent small town mayor and wife of the popular high school principal? Linda and Kevin Lusk were one of the most respected couples in Prosser, Washington until the unimaginable happened: Linda was accused of sexting and having inappropriate physical contact with a 14-year-old high school student who also happened to be her daughter's ex-boyfriend. It became a small town scandal that spread like wildfire. After a police investigation was launched, followed by a media firestorm, the once golden couple was under siege. Linda admits that what started out as a maternal and nurturing relationship with the boy, nicknamed Bubba, turned terribly wrong after his friends dared him to make Ms. Lusk his first conquest. But how much of the story was true, how much was a high school kid's boastful "kiss and tell" and was Linda's depression, stemming from her grief of losing her disabled 15-year-old son, really to blame? "20/20" is behind the scenes with the family at the center of the small town scandal as they deal with the aftermath of a lunchtime encounter. Chris Cuomo reports. (OAD: 11/11/11)