Secret life turns inward to our human habitats to reinvestigate the creatures and organisms we "control" or take for granted. After realizing her excursion to antarctica felt awkwardly structured and artificial, the author becomes enamored with a lichen species that she comes to realize actually thrives at home in her own city. With this small revelation she decides to start looking for "the wild" within the urban. Crows get their own chapter, as do songbirds (did you know urban songbirds start singing a few hours earlier and that their cries are louder and a higher pitch to be better heard?), gulls, ants, bats, and organisms.
Her main thesis is that the animals that live in the city evolved to be close to humans and have literally evolved to be less afraid of us so you can actually really see them in their element in a way you never can in the wilderness. And that there's an intimacy to becoming familiar with the lives that provides intrinsic value. That nature, essentially, is everywhere we look for it and not simply an abstracted and distant experience mostly seen on trips and television.
A lighter book, with an easy but pleasant writing style. It has a lot of personal anecdote and is mostly more nature writing than science, although there's a decent amount of that as well. Very enjoyable.