Mary Margaret is convinced she’s a mermaid, or, at the very least, that she can become one. Her grandfather, the only caring male in her life, has recently died, and she is taking her grandfather’s place, accompanying her grandmother on a senior citizen’s cruise through the Greek islands. Armed with glittery pens and a new journal, she writes of her experiences with some eccentric fellow travelers, her concern for her grandmother, her own grief, her impressions of the various ports of call, her very own seven wonders of the world, and, of course, the mermaid issue. Mary Margaret is an absolutely delightful fourth-grader, who is at once childlike and alarmingly precocious. Hazen has written a charming account of a girl’s voyage that includes not only the latitude and longitude but the discovery of some of the meaning of life, love, and family. A winner. (Fiction. 7-11)