Heart is sure that the small book she found in Lord Dunraven's castle holds the secret to finding a safe haven for her beloved unicorns, Moonsilver and Avamir - especially after a village blacksmith tells her about a pair of ancient iron gates that are decorated with the same unicorn motifs that appear in the book. Will the book also unlock the key to Heart's own memories and help her discover who she really is and where she came from - are the unicorn motifs on the gates the same as those on her blanket and in the book? What is on the other side of these gates and where does it lead to? As Heart struggles to learn how to read she knows that she must continue to protect the unicorns, but this is becoming harder and harder as Lord Dunraven's men close in on them...