While walking around her house , Thea finds a map in her room of Gracehope . The map shows a tunnel leading onto the surface . Thea and her cousin Mattias find the tunnel and meet Peter who helps them back to Gracehope . Reaching Gracehope , Peter realizes that several talismans of the people are in the shape of mitochondrial DNA , which his mom is studying . After waking up from a headache , Peter finds his mom next to his bed . She explains that she used to live in Gracehope , but was banished with her sister , after her sister ventured above the surface and contracted an illness that could not be cured . She also explains that her research of mitochondrial DNA relates to the ability of mutations to benefit the human body , which could cause their extremely good vision and hearing . In the end , she warns Peter that global warming is causing Gracehope to slowly melt away . The entire colony must learn the dangers they face and escape . One obstacle lies in their way : Rowen , Thea and Peter 's grandmother who banished Peter 's mom and did nothing to help Thea 's mom when she was on her deathbed from an illness when she ventured aboveground . Rowen is the head of the Council in Gracehope and is strictly against going aboveground .