MAMMOTH revolves around successful New York couple Leo (Gael García Bernal) and Ellen (Michelle Williams). Leo is the creator of a booming website, and has stumbled into a world of money and big decisions. Ellen is a dedicated emergency surgeon who devotes her long shifts to saving lives. Their 8-year old daughter Jackie (Sophie Nyweide) spends most of her time with her Filipino nanny Gloria (Marife Necesito), a situation that is making Ellen start to question her priorities. When Leo travels to Thailand on business, he unwittingly sets off a chain of events that will have dramatic consequences for everyone.