What is the theme in Through the Tunnel by Doris Lessing?

Rites of passage is a theme. Jerry's beach vacation becomes the site of an intense personal challenge. Jerry must leave his mother at the shore, the shore Jerry sees as "a place for small children, a place where his mother might lie safe in the sun." He leaves the safety of this nursery-like beach and journeys to the treacherous "wild and rocky" bay and the underwater tunnel. An eleven year-old nearing puberty, Jerry is fatherless and approaching adulthood as the sole male of the family.