William Trevor just keeps on going. Alternating between short stories and novels, the master Irish fiction writer seems to be reaching the heights of his powers. His new story collection, "A Bit on the Side," mines much of the same turf as his past works: the characters are usually heart-broken, reserved members of the Irish middle class. And yet, Trevor always seems to come up with new ways to startle the reader, to reveal devastating details in seemingly mundane scenes. Two lovers drift into and out of each other's lives in the outstanding story "Graillis's Legacy" "The winter flowers lay scattered in the shadow of a secret," the story concludes, "deception honoring a silent love." "A Bit on the Side" comes after Trevor released perhaps his most acclaimed novel yet, The Story of Lucy Gault. Lucy was a young Protestant girl in Ireland whose parents fell out of favor with local revolutionaries. When the Gaults mistakenly believe their daughter has died, they pack up and move to the continent. The trouble is that Lucy is very much alive. The twist worked, and the Cork-born author had as good a novel as his earlier work Felicia's Journey. With "A Bit on the Side," Trevor's short story fans can rest at ease. He remains a master of this form as well. ($24.95 / 245 pages / Viking).