While tracking a young boy with dangerous powers, Dr. Helen Magnus encounters Will Zimmerman, a psychiatric resident who may have what it takes to become her new protg.

Will Zimmerman is drawn further into Magnuss mysterious world and finds himself confronting his oldest fear. Elsewhere, forces converge on the target of their hunt including someone from Magnus distant past.

The origins of the mysterious mutant boy are revealed, as is the relationship between Magnus and her old flame John Druitt. Ashley, meanwhile, seeks out Ernie Watts a weapons dealer and fellow monster hunter extraordinaire only to find herself in mortal danger.

Helen and Will confront John Druitt with deadly results for a member of the Sanctuary team. Ultimately, Will is forced to choose between his old life and the strange world of Dr. Helen Magnus.

While investigating an ancient crypt on a remote island, Magnus and her team encounter deadly creatures and three women with a mysterious past. Ashley decides to address the issues of her father's existence head-on.

The investigation into the three women found in the crypt continues, confirming Magnus' theory that they are much more than they appear. Ashley's hunt for contraband creatures yields mixed results.

Will falls victim to the three women's growing powers, while Magnus seeks proof of their true identities via a former resident of the Sanctuary. Ashley's luck in her monster hunt begins to run out.

Magnus, Will and Bigfoot defend the Sanctuary against a deadly assault, while Ashley struggles to survive her encounter with a nearly unbeatable foe.