OVER THE PAST 25 years David Watmough has chronicled the life of his alter-ego, Davey Bryant, a Cornishman transplanted to Vancouver. Now, in what is literally his biggest book, Thy Mother's Glass (HarperCollins, 308 pages, $24.95 cloth), Watmough seeks an answer to the big question: how did Davey get to be who he is?

The story begins in 1916, with Davey's mother. She was a chemist whose career ended when 50 tons of TNT exploded in her laboratory; as a married woman she sent Davey to live with an aunt and uncle during the war. That "abandonment" is the central event in Davey's life.

The book is a little like Portnoy's Complaint, but without the graphic sex the self-examination without the self-abuse. Davey perceives himself a product of his mother's coldly methodical nature, although his lover, Ken, claims that Davey has "invented" this version of her. The paralleling of these two lives occurs at a contemplative pace, told in alternating passages of the voices of Davey and his mother, through diary entries and letters over a 50-year period.

Watmough does not retell those stories of Davey's life that he has told elsewhere and, while the missing details are not necessary to the construction of Thy Mother's Glass, I felt in places that their absence made the narration seem slightly evasive, as though Davey were being less than forthcoming. Readers of Watmough's previous fictions will be able to fill in the gaps, however, and new readers may want to return to the stories.