With the new Abnormal Homeland now openly under threat, Henry and Tesla learn that the SCIU weaponized Tesla's work to use against Abnormals. Bigfoot and Kate investigate Caleb's rise to power while Will and Abby look into Magnus' past.

Magnus has pursued Adam Worth back to 1898 London to stop him from altering and quite possibly completely destroying the future. As she battles to stop Worth, stay hidden from her past-self, and avoid taking any action that might change the events of history, Magnus must also figure out how to get back to her own present day timeline.

Magnus flies to a remote island in Africa to meet with the Sanctuary's new top secret advisor, but lands herself in the middle of a deadly hostage situation.

Magnus is approached by a notorious leader in Hollow Earth who is looking for assistance in building a new home on the surface for his insurgents, but problems arise when the world's government gets involved. Addison reactivates Will's federal commission.

The team tracks an аbnormal fugitive, and discovers that Tesla is the head of a secret research lab for a Homeland Security agency that conducts tests on Abnormals.

When a team from the UK Sanctuary gets in trouble on a stranded icebreaker in the Bering Sea, Magnus and Will must figure out who is behind the mysterious happenings at sea.

Just when Magnus thought Adam Worth was gone forever, she and Tesla become trapped in a virtual Sanctuary, where they are attacked by an avatar of Worth – who is determined to enter the “real” world.

Kate returns from Hollow Earth with word that insurgents are about to strike an above-ground target – and may have inside help from a trusted member of Team Sanctuary.

As Hollow Earth Abnormals continue to arrive at the surface in droves, Will, Henry, Kate and Bigfoot scramble to prevent all-out war with the Lotus Security Forces. All the while, they are worrying about the whereabouts and safety of Magnus who was last seen heading to Praxis just before the city was destroyed.

With a government inspector threatening to cut off the Sanctuary's funding, Magnus and Will must explain a mission gone wrong. Meanwhile, Henry has a surprise visitor with some shocking news.

A quest to capture a legendary Abnormal in Bolivia leaves Will and Magnus injured and trapped in a cave-in, where they confront truths about themselves and their relationship. Henry records video letters to a special someone while working on an invention.

Will runs into unexpected trouble and personal revelations on a trip to the Liberian Sanctuary in Monorovia. Meanwhile, Magnus has her hands full when a couple of ne'er-do-well flying Abnormals recruit her help with a questionable scheme.

A mysterious abnormal attacks Abby, and Magnus and Will discover there's only one way to communicate with this unusual enemy - through music.