While looking for a class project, Lisa Duncan finds a diary in a sea caption?s home that his wife had written years ago. The diary tells about how she waits for her husband to return home, standing under the unicorn tree as she watches the ocean for his ship. Because Lisa?s brother is sailing on a tall ship and is lost at sea, Lisa feels an affinity for Mirabelle and sets out to find the unicorn tree, with Mirabelle appearing to her to guide her way. Lisa searches for her place in life just as she searches for the unicorn tree.