凯瑟琳（琳达·汉密尔顿 Linda Hamilton 饰）是一位精明强干的律师，某日，她遭到了歹徒袭击，身负重伤，昏倒在公园下水道里。就在这时，一名长着狮头的怪异男子出现了，他将凯瑟琳带回了自己位于底下的家中，细心地照料她的伤势。原来男子名叫文森特（朗·普尔曼 Ron Perlman 饰），在地下还生活着很多和他一样的人。

一名用爪子杀人、让受害者看起来像被熊咬伤的杀人狂正在四处游荡。他在地铁上发动袭击。他的大部分受害者都比较年长。当凯瑟琳发现这个案子时，她开始怀疑文森特，因为她记得文森特是如何在安全屋把她从袭击者手中救出来的。她和他谈了这件事。在某种程度上这让他很不安，但他告诉她那不是他。当她确定不是他时，她松了一口气。特别是因为真正的罪魁祸首是一个非常意外的来源。

Vincent is blinded after an explosion and must escape a street gang that is holding him hostage. Once he is free he must find his way home.

Halloween night Vincent goes above to meet an Irish writer named Brigit O' Donnell. Halloween is the only night that Vincent is safe above. Catherine is at the same party. Eventually they wind up spending the evening together as Catherine shows Vincent her world.

Catherine has a nearly fatal confrontation with an ex-tunnel dweller, named Mitch Denton.

Vincent is captured and held hostages by two scientists who stick him in a cage. Catherine considers a new job in Providence.

Father's past is revealed when he goes above for the first time in over thirty years to see a friend. When he gets to his friends office he finds his friend is dead. Father is then charged with murder.

An investigation into the mysterious death of a wealthy business man leads Catherine into the world of voodoo. After her apartment is vandalized and she is terrorized, Vincent seeks the aid of Narcissa in an attempt to understand what is happening to Catherine. When the voodoo priest attempts to sacrifice Catherine, Vincent comes to her rescue, starting a fire when he pushes over the altar table. Mistaking Vincent for his god, the priest walks into the fire and is destroyed.

Vincent alerts Catherine to possible wrong-doing at a well-known, renowned orphanage. Her investigation leads to the discovery of a child-selling scheme operated by the orphanage's owner and a thief who uses the children to steal for him. Catherine rescues a brother and sister (Eric and Ellie) and takes them to live in the tunnel world.

Laura, a deaf-mute tunnel dweller, witnesses the murder of a police officer, for which another man is framed. She goes above with Catherine, but is kidnapped by the real murderers, who are also police officers. Cuffed to a pipe in the basement of the murderer's house, Laura taps out an SOS, which is heard by Pascal and Vincent rescues her. She decides to return Above to live.

Attempting to aid an injured child (Eric) in the Maze, a cave-in traps Vincent and Father. Catherine, after facing Elliott Burch, who has agreed to be a witness against an extortionist, senses something is wrong and rushes to the tunnels. When her attempts to contact someone fail, she wanders the tunnels, tripping a trapdoor which sends her tumbling down to Mouse's quarters. He leads her to the others. Mouse can save Vincent and Father, but needs demolition supplies. Catherine goes back to Elliott Burch, who gives them to her, no questions asked. Mouse succeeds; Vincent and Father are freed. Father is much more understanding of Vincent and Catherine's relationship. Catherine tells Vincent she loves him and he watches her as she returns to her world.

SYNOPSIS: ""Romeo and Juliet"" are in Chinatown. An angry Tong invades the tunnels with his army.

Paracelsus, a former friend of Father's, sells an hallucinatory drug in the world above.

Vincent and Catherine prepare gifts for the celebration of the anniversary of the day they met. Joes is distracted by a beautiful woman named, Erica Salvin.

Vincent's foster brother, who is also Father's son, Devin, returns to the tunnels after a 20 year absence.

Steven Bass, Catherine's ex-fiance resurfaces. He has all ready been in a mental institute and is very strange. Vincent has dreams of disaster connected to Catherine. He warns her but she thinks that he is paranoid or jealous. When trouble does come to her Vincent is right there.

While exploring a section of the tunnels Mouse discovers a treasure ship. Cullen's greed brings strife.

After faking that Catherine hit him young Tony Ramos winds up living with Catherine. She tries to help him by talking to Vincent. Vincent tries to help as well. But it is Tony who winds up trying to reverse unjust banishment of his family before a Gypsy court.

Paracelsus kidnaps Catherine, which causes Vincent to begin a quest to rescue her.

Construction of the Birch tower is causing many problems in the tunnels. To help the problems stop Catherine agrees to marry Elliot Birch. This should halt the construction of his tower and also leave the tunnels as a safe place once again.

Catherine's pain about her fragmented life almost causes her to end her relationship with Vincent.