Mallory Greenleaf is the protagonist of Check & Mate. The novel is told from her perspective and follows her journey from an ex-chess player and the breadwinner for her family to a majorly successful professional chess player. Her most striking physical feature is her pale blond hair, a trait she shares with her two younger sisters. Mallory is highly intelligent and determined. Despite her acceptance to colleges alongside offers of scholarships, she refuses to leave her family, as her mother is often too unwell to earn the money needed to support the family.

Mallory excelled at chess as a young girl under her father’s tutelage; however, she abandoned the sport after her father’s affair and her parents’ divorce, angry with her father and with the sport that he taught her to love. In the years since, Mallory has become emotionally reserved, protecting herself both from others and from the pain she experienced after her father’s betrayal and subsequent death. She also resists relationships to avoid the betrayal she sees as a result of such commitment, keeping herself free to care for her mother and sisters.

Although the tournaments of professional chess provide important outer conflicts for Mallory, her primary conflict is an inner one.