The series is named after a small part of Saltsjöbaden called Solsidan. It revolves around Alex and Anna who are expecting their first child and have just moved to Alex's childhood home in Saltsjöbaden, Stockholm County. Alex tries to get Anna to enjoy herself, and at the same time spend time with his childhood friend Fredde.

Hundred years ago, three students at the Hellestads Boarding School were brutally slaughtered, the murderer drowned himself in a lake nearby and his body was never found. The story has become a legend for generations of students as well as a yearly festivity. Sara, a student, is writting an essay based on the legend and uncovers new facts from the event that will cast dark shadows on the family name of one of the school's main benificiaries. On the night of the hundreth anniversary, the festivities go awry, students disappear and something dark and unknown is moving through the schools corridors...