The year's best still providing the best entertainment in this form, and certainly experience lends expertise to Roy Vickers Double Image, in which an identity as well as a life is destroyed: the fatal irony of Margaret Millar's The Couple Next Door; the grim sobriety of Dorothy Salisbury Davis' Backward. Turn Backward; while a murder trial accelerates the pitch of John Ross MacDonald's Wild Goose Chase. Stanley Ellin, Margery Allingham, A.Z.H. Carr, Philip MacDonald, and James Yaffe are old familiars, while among the newcomers- Henderson and John Hayward have youngsters to heighten the appeal of You Know What, and Heat Spell.... As always, a select selection.