Lowry introduced Matty in Gathering Blue; he is an energetic and impatient individual who is undergoing a transition into adulthood as the story begins. Matty lives with Seer (originally named Christopher), an "unseeing" man who the people of the Village rescued years before. Matty is desperate for his new name to be "Messenger," which is what he feels he is best at doing.
Many of the people in Village are like Seer: cast out from their old communities and sometimes seriously injured. They have made themselves new homes in Village. Most of the Villagers are reasonably altruistic, and the Village never lacks in people who are willing to help another Villager overcome some disability. Matty is from a community wherein people only know what the community tells them, and where those who do not fit the norm are usually put to death.
Outside the safe boundaries of Village is Forest, a foreboding realm which most of the Villagers fear. In spite of the lack of dangerous beasts, Forest itself is animated. It is capable of delivering "Warnings" in the form of injuries caused by such things as sharp twigs, stinging insects, or poisonous plants, all of which attack with deliberate intent if Forest is entered. If the person who was warned enters the Forest again, the Forest will kill them. Matt, whom Forest seems to favor, has gone through Forest many times without incident. Consequently, he has become Village's messenger, carrying word to the other communities scattered throughout the region. At one point, Jonas (called "Leader" in this book) says that he received a barge full of books from the Community, and that the Community has changed.
Very early in the book, discord appears in Village. People who trade at a gathering called Trade Mart change from compassionate and generous to angry and impatient. The temperament of the Villagers changes, and they decide to close their borders, no longer permitting the displaced and unwanted of other communities to enter. Seer, in the wake of this sudden change, decides to send Matty to travel through the Forest to retrieve his daughter, Kira, who lives in a town several days away. The journey soon becomes gravely perilous, as the Forest begins to attempt to entangle Kira and Matty. Leader's ability of remote viewing, which the book often refers to as "seeing beyond", allows him to sense the danger. He enters the forest to save them, only to be captured himself. Kira, who has the ability to weave prophecy-like patterns in thread and cloth, uses her gift to contact Leader, who tells her to have Matty use his gift to save them.
This gift is a special ability which Matty possesses but hardly understands, which makes him mad, resulting in a fury; a power of healing, which causes wholeness from the inside out. Matty puts his hands to the ground and manages to restore the integrity of Forest and people alike, at the expense of his own life. Leader names Matty the Healer.
Near the end is a quotation of poetry, derived from To An Athlete Dying Young: "Today, the road all runners come/Shoulder-high we bring you home/And set you at your threshold down/Townsman of a stiller town." This is spoken by the Village's schoolteacher, known as Mentor.
On a side note, in the previous book, Gathering Blue, when Matty was a child known as Matt, the nursing of his dog Branchie back to health could be a possible foreshadowing of Matty's healing powers. In this third installment of The Giver Quartet novels, it is implied that some of the citizens in the Village are or know Jonas, Fiona, Gabe, and The Giver.