The enigmatic Dr. Helen Magnus recruits insightful forensic psychiatrist Will Zimmerman to join her in the quest to track, study and protect the strange and often terrifying creatures that secretly populate our world.

A forensic psychiatrist is on the trail of an odd boy who left a crime scene, and comes upon a doctor with a strange proposition.

Dr. Helen Magnus, her daughter Ashley, and the newest member to the Sanctuary, Dr. Zimmerman, travel to Northern Scotland to discover three women in an ancient crypt and bring them back to the Sanctuary for refuge and study.

While investigating a series of strange robberies, the Sanctuary team encounters a group of thieves, who seem to possess a strange ability which apparently allows them to literally slip between the cracks of the law.

While returning from a trip in Himalaya meant to capture an abnormal, Dr. Magnus and Will's plane crashes in a remote mountain range. But it soon appears that struggling to stay alive and wait for rescue is not the only thing they need to worry about, as the surviving passengers fall one by one to an unknown assailant...

When two seemingly harmless abnormals arrive at the Sanctuary, the team finds themselves feeling some unusual animal attraction for one another...

When Magnus encounters an old acquaintance in Rome, he tells her that the Cabal is planning to seek revenge on her for the events of "Fata Morgana". But she soon learns that his loyalty is not as intact as it was in their earlier days, when they were both part of a group called "The Five", within which members are connected by a secret protected for ages...

Detective Kavanaugh asks for Will's help in a sleeping case that he feels is suspicious. An autistic boy named Edward seems to be involved and it later emerges he has an unusual gift, he can draw images from memory at great speed and that are incredibly detailed, almost as if they are photograph's.

Magnus and Will set off to the Bermuda Triangle to answer a distress call they received from one of the abnormal species living there. They use their sonar equipment to try and contact the abnormals in their underwater home but find they are too late.

When Danny, and old friend of Will goes missing, his wife contacts him asking for help. With the aid of Helen and Ashley, Will starts searching and they find themselves in an abandoned factory. There is no sign of people, but the team come to the conclusion that something took place there after they find dried blood and the drug epinephrine. They come to the conclusion that the building is being used as a place to train fighters.

Desperate to get their first exclusive news story Amy Saunders and her cameraman Zach Spencer get inside an evacuated building. Earlier that day three people had been found inside, brutally cuddled by a strange creature. With the police trying to handle the delicate situation the duo go in search of the culprit, but they are completely unprepared for the powerful beast that they find.

Magnus and her team have to face the possibility of international biological warfare when a virus infects the abnormals, causing them to attack humans. John Druitt makes an unwelcome return to the Sanctuary as, he too, sees the significance of the situation and he tells them the Cabal are behind it. The leader of the UK sanctuary, Sir James Watson, contacts Helen and confirms John's story about the Cabal, meaning she has to work fast.

Ashley and Henry are captured by the Cabal after breaking into their weapons factory. While being restrained Ashley learns from Dana Whitcomb that the plan they have for the virus to be released worldwide will still go ahead. In a different part of the facility Henry is being kept strapped to a hospital bed. The Cabal intend to use chemicals to turn him into his abnormal state, and keep him that way.