"Two Hearts" is a story that takes place many, many years after The Last Unicorn. A griffin has made its home near Sooz's village. It's a minor annoyance until it starts taking children. A few knights are dispatched, but they all die. After the griffin takes Sooz's best friend, she sets off to find the king. She meets Schmendrick and Molly Grue on her way; the pair of them take her to King Lir's castle. But Lir is an old man now who gets confused. Although he agrees to rid Sooz's village of the griffin, everyone fears that the king will not return, especially since he has to strike both of its hearts to kill it.
I apologize that I'm half asleep as I write this, and not feeling at all articulate. I really liked reading about the further adventures of Schmendrick, Molly, and Lir. And Sooz was a fun character as well. "Two Hearts" was an interesting yet satisfying epilogue to The Last Unicorn. I'm super glad to have read it.