 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 <unk> find the tunnel and meet Peter who helps them back to Gracehope . Reaching Gracehope , Peter realizes that several <unk> 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 <unk> . Rowen is the head of the Council in Gracehope and is strictly against going <unk> . 
