What You Wish For: On Christmas Eve by Ann M. Martin

It's almost Christmas of 1958, and her sister Evvie tells Tess that it's time for her to give up her belief in Santa. Still, as the holidays near, Tess feels the old magical pull of Christmas Eve and Santa's coming. Surrounded by the comforting mid-century rhythms of the season--fashioning homemade ornaments, cutting a Christmas tree, hanging the old string of golden lights, and watching her big sister portraying the angel Gabriel in the church pageant--Tess's anticipation is saddened by the serious illness of her best friend Sarah's father.

Still Tess catches glimpses of the magic that she hopes to see if she can just wait up til Santa comes, when she can make known her wish, not for herself, but for Sarah and her father:

"We are excited, but for very different reasons. I don't say anything about this to Evvie, though. Evvie does not believe in Santa, or in the magical world that is part of our everyday world--the one that is there sort of, at the edges, something you might be able to see out of the corner of your eye if you turn to just the right place at just the right moment. If you truly believe."

Tess gets her magical moment at midnight and makes her wish for Sarah's father, although even on Christmas Eve Santa can make no promises that all wishes will be fulfilled.

In On Christmas Eve (Apple Signature Edition) Ann M. Martin manages to weave Christmas magic with a minimum of sentimentality and plenty of genuine feeling in this brief novel which walks the line between realistic fiction and fantasy.