Years later, she has used those convent ruins as a key backdrop for “How to Get to Heaven From Belfast,” a zany murder mystery that debuts Thursday on Netflix. The show follows three millennial women who were childhood besties — Robyn, Saoirse and Dara — as they investigate the untimely death of their estranged fourth muskateer, Greta. Across a galloping eight episodes, the gang encounters a whole host of zany obstacles and characters — and the universal, painful question of what we owe our younger selves.