This book traces the cultural and mythological story of ubicomp - the idea of Ubiquitous Computing developed at Xerox PARC in the eighties by a team led by Mark Weiser.
Bell and Dourish are exploring the mythology of ubicomp as a way to understand the "ideas that animate and drive ubicomp forward."
They don't mean mythology in the sense of a false myth, but instead as the kind of cultural mythology that helps us (humans) organise the world around us and express our values.
"Myths are stories that animate individuals and societies by providing paths to transcendence that lift people out of the banality of everyday life. They offer an entrance to another reality; a reality once characterised by the promise of the sublime"
The ubicomp agenda emerged in a particular time, place, and culture, and has a set of specific ideas about what what technology can do for people, the places it will go, and the needs it will address.
Mark's 1991 article in Scientific American, The Computer for the 21st Century is essentially the Biblical founding document here.
In it, Weiser outlines a vision for a kind of computing where "technology recedes into the background of our lives." Rather than focusing on improving computer interfaces themselves, Weiser wanted interfaces to dissappear altogether. To get out of people's way and seamlessly blend into the background of their lives.