An anomaly in the wine cellar of a wedding venue opens and a family of Hyaenodon comes through. A male, female and three cubs are in the cellar when the wedding planner (Norma Sheahan) comes downstairs. She is attacked and killed. Upstairs preparations continue.
At ARC the anomaly detector goes off and Connor (Andrew Lee Potts), Abby (Hannah Spearritt) and Matt (Ciaran McMenamin) are sent to investigate. Since Ethan (Jonathan Byrne) is still on the loose, Matt takes Emily (Ruth Bradley) with him. They find the anomaly and lock it. They find a Hyaenodon, subdue it and send it back through the anomaly. Then they find out that the wedding upstairs is for Jenny Lewis (Lucy Brown). They assure her that they have dealt with the problem, but they are unaware that there are still one more adult and three cub Hyaenodon roaming around.
Meanwhile Becker (Ben Mansfield) decides to track down Ethan. Believing that Ethan would stalk Emily before kidnapping her he checks out the nearby buildings and finds out where he had been staying. Thinking that Ethan will return he stakes out the building. Jess (Ruth Kearney) shows up with food and keeps him company while he waits. When he sees Ethan enter the building, Becker goes in and hits a tripwire connected to a bomb.
Gideon (Anton Lesser) dies from his illness. We find out that Gideon is Matt’s father.
Episode 6 of season 4 features Hyaenodon. Hyaenodon were fast and vicious dog-like carnivores which lived from the Late Eocene to the Early Miocene of the Cenozoic era.