In the second-season opener, a young mother and her babies vanish, and their disappearance may be linked to that of a second missing mother and child.

Detectives Selles Morris, Laura Skrip and Jim Corcoran team up to search for a straight "A" college student. They uncover surveillance footage that shows the 19-year-old sophomore walking toward the lakefront, then disappearing. Their around-the-clock search comes to a shocking conclusion. Then, Detectives Morris and Skrip pull double duty: Morris hunts down an alleged gang member who vanished after a drug deal goes bad, putting his own family in danger. Skrip has just minutes to save the life of a woman who threatens to jump from a bridge.

When a caretaker reports her 63-year-old cancer patient missing, Detectives Ayanna Corbin and Mike Cochran learn the woman has left behind a 15-year-old son. Detectives sift through false sightings, deceitful witnesses and a missing mattress.

Detectives Laura Skrip and Joe Struck hunt for a man after his family receives a threat to his life. They must sort through the missing man's troubled family situation and possible drug connections. Next, during a summer of gang violence on Chicago's streets, Detectives Mario Gonzalez and Hector Crespo search for a teenager with a rare sleep disorder. He vanished after getting into a fight with a group of boys. Detectives race to find him before he becomes another casualty.

Detectives Pam Childs and Selles Morris search for a 14-year-old girl who has been snatched by a 19-year-old with possible gang connections. The hunt leads detectives to a hotel district at the edge of town, through gang territory and across the state. Meanwhile, on the hottest day of the year, Detective Pat Riley searches for a missing 66-year-old man with serious neurological problems. Riley fears the man may be armed. The clock ticks as the thermometer tops 100 degrees. Riley must find the missing man before he succumbs to the heat--or gets into real trouble.

Detectives Selles Morris, Judy Rolston, and Jamie Duignan are on a frantic search for a missing 17-year-old girl and her 2-year-old baby... and every minute counts. The baby is epileptic and without her daily medication she could suffer a fatal seizure. Meanwhile, Detectives Nari Isaakson and Jose Diaz race through some of the city's toughest neighborhoods looking for an 86-year-old man who vanished on the way to a Christmas party. He suffers from Parkinson's disease and dementia. With a blizzard barreling toward Chicago, detectives have only a few hours to find him.

With Mother's Day approaching, Det. Bob Berent meets with another anguished family. The son and daughter of a 48-year-old Iraqi immigrant returned from work to find her gone. She has no ID and no money, and her children believe she may have delusions that she can return to Baghdad. Det. Nari Isakson joins a search that spans from forest preserves to O'Hare Airport. Meanwhile, Detectives Pam Childs and Joe Struck hit the streets in search of a 48-year-old woman. Her two grown daughters fear she is the victim of foul play. As Childs and Struck interview witnesses and possible suspects, they uncover startling new evidence: it's clear that someone knows something.

Every available detective hits the streets when a talented 30-year-old vanishes on his bicycle, just weeks after earning his second Masters degree. Detectives Jim Corcoran and Beth Svec must find out whether the missing man could have died in an accident... or was kidnapped by an old acquaintance. Detectives Selles Morris and Pam Childs join the search as the team sorts through misinformation and false leads. They must untangle the missing man's past to uncover what really happened to him.