Lore by Alexandra Bracken

""Lore" is a standalone young adult fantasy novel that weaves together elements of Greek mythology and modern-day New York City. Every seven years, the Greek gods return to earth and hold a deadly competition called the Agon. Lore Perseous has distanced herself from this world, but when a childhood friend seeks her help, she is drawn back into the dangerous and treacherous game where gods and mortals battle for power. As Lore navigates this brutal contest, she must confront her past and her family's dark legacy.