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Candice, Evan, Grace, Toby, and Tyler continue their journey through the Upper World and come across a mysterious broken portal. Travelling to a mysterious and amazing part of the Underworld they have never seen before, the gang looks to Grace, an expert in the Underworld, for help. However, as they face new challenges, Grace realises that she is not up to the pressure of the team! They find themselves deep in the bastion and have to face their toughest challenge yet... without their expert. It's going to take all the power of the team to overcome the unknown!