A Ring of Endless Light — Madeleine L'engle

Watching her grandfather's condition deteriorate as the summer passes on beautiful Seven Bay Island is almost more than Vicky Austin can bear. To complicate things, she finds herself the center of attention for three very different boys: Leo is an old friend longing for romance; wild Zachary is sophisticated but troubled; and Adam, her older brother's friend, offers her a wonderful chance to assist in his experiments with dolphins but treats Vicky as a young girl just when she's ready to feel grown-up.

Why is life so hard when you're a teenager? Vicky wonders. But this summer she discovers that past the darkness of tragedy comes the light of joy.