Irish writer Boylan opens her fourth novel with a biblical epigraph: ''Be not forgetful to entertain strangers: for thereby some have entertained angels unawares,'' and the theme reverberates throughout this engaging tale. In an unnamed Irish city, Dinah, a big-hearted black woman with a lust for life, winds up on the doorstep of Alice, a fearful 67-year-old spinster. As Dinah recounts her mythic (and mythical) past, Alice comes to believe that Dinah is the black baby she ''bought'' for a missionary donation when she was 12 years old. She welcomes Dinah as her daughter, and Dinah breathes new life into Alice's dull existence. Boylan writes with sureness, aplomb and humor; her metaphoric language crackles with exactitude. She never succumbs to sentimentality or quaintness, even when dealing with subjects as potentially dangerous as brotherly love and the loneliness of old age. Despite the somewhat heavy-handed ironic ending, this is a delightful read.