Lilly re-opens the 1929 case of a woman found dead in a ravine on Christmas Day when the victim's great-granddaughter comes in asking for help. Meanwhile, Lilly's estranged mother shows up, hoping to re-connect with her daughter.

The team re-investigates their oldest cold case yet, the 1919 murder of a young woman who was a passionate advocate for women's right to vote.

The 2005 murder of a longshoreman who accidentally became involved in a human-trafficking ring run by the Russian mob.

The 1998 death of a terminally ill man who died months before he was expected to is investigated after a nurse confesses to six so-called mercy killings.

In the fourth season finale, a hostage situation arises when the entire team is held captive while they're investigating the 2006 killings of a family who had just moved into a new house.