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.

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.

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.

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.

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

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.

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.

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.

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.