In "New Beginnings," the Season 5 premiere of this hit medical drama, Shaun and Lea's (Freddie Highmore, Paige Spara) engagement party has all their friends and colleagues in a festive mood after they return from Guatemala. Meanwhile, a single mother is stunned to find out that her cancer-stricken son may have contracted his illness from an unexpected source, and Mateo (Osvaldo Benavides) learns whether his previous issues in America will be resolved.