A young woman, Karen, is studying psychology at Cambridge University. She finds an iPhone in a waste basket years before its invention. Years later, the owner's father claims the phone. His son has gone missing. Karen and a detective in Edinburgh suspect Tom has joined psychological experiments using psychedelic drugs. His girlfriend anxiously wants to find Tom, and they suspect a professor at the university because he develops algorithms that cause smartphone addiction. The CI and Karen discuss time travel, out-of-body experiences, and Celtic and Viking mythology, suggesting time is circular, as Celtic stone circles symbolise. Only travels to the past are possible. They discover a circular tunnel system at St. Bernhard's Well and the well cave at Wemyss, where the CI finds Tom's fingerprint. The CI and Karen believe Tom wanders in circular tunnels, adjusting time to his body. Tom appears in poor condition and tells his story about a medieval document. The friars and two professors start an experiment to cure smartphone addicts by entering the tunnels at Halloween. Below St. Mary's Cathedral, they discover the mythological Urdarbrunnr and try to rid the tunnels of its ghosts but barely escape. The phone is recovered, but memories are lost.