Zoology student, Xenia Sweet, believes that she has captured images of a rare black, or melanistic, jaguar, commonly known as a black panther. Wild jaguars no longer exist in North America. . . Or do they? Xenia manages to convince park ranger, Dale Marquez, to help her find the elusive creature. Dale thinks he has found his remote, bone-littered, den under an abandoned railway boxcar that is now headed to a railroad museum near Chicago. Is the jaguar in the boxcar? Hundreds of miles away in the Chicago area, Sara Williams, orphaned from an auto accident in Alton, continues to scheme to get Mike Kellogg, a Cryptozoologist, to adopt her. If he does, she can remain close to her best friends Emily Peters and Krystal Rogers. Meanwhile, Mike’s planned research trip to Tasmania, with fellow Cryptozoologist, Liz Newcastle, is sidelined when the Cryptozoology Museum decides to do an exhibit on Melanism. At the advanced preview for Mike’s guests, which includes Xenia and her sister Pamela, two lion-sized cats suddenly appear in the museum on Chicago’s downtown lakefront. Xenia thinks they are the jaguars from Arizona or possibly an extinct American lion species called the Atrox. Mike thinks they are simply some type of hybrids. In the midst of a thunderstorm, Xenia, with Pamela and Liz, join Mike, Sara, Emily, Krystal and others, including the Chicago Police, in a race to find, identify, and capture the animals before they can wreak havoc on the lakefront.