Barker, a veteran British writer little known here, recognizes that minute pressures, something as delicate as a ""heavy feather,"" can send lives spinning; her loosely-twined, very English, coolly perceptive new novel strings out a clutch of examples through nine episodes in the life of Almayer Jenkins. Brought up by her plumber father after her disheartened mom deserts, Almayer takes piano lessons from the eccentric Miss Velma, and from a generally disordered childhood learns to recognize people at their most crucial moments of strayness. As a young woman on her own, Almayer finds herself the wedge between a homosexual couple, David and Georgie. And while the man she finally marries, Clarence Burgoyne, is stolid as porridge, one of their three children is brain-damaged. Barker shifts the book here from gently dotty to really dark, taking on a great poignant strength that emphasizes the slippery slightness of the preceding chapters. But the tone throughout is assured, amused, and reflective--even when at half-throttle.