Sister Agatha is a colossal 118 years of age, whose vim and vigour would put the most robust athletes to shame. During a routine check-up, however, her doctor claims she has just a week to live, news that proves to be quite inconvenient, seeing as the beloved sister has one ambition in life: to be the oldest person in the world. At last count, she was the fifth. However, never one to admit defeat, Sister Agatha concocts a bold Plan B. Dusting off her passport, she decides to leave Irish shores for the first time in her very long life, and using the few days remaining, plans to travel across three continents and meet the only four people whose birthday cakes boast more candles than hers. And then, one by one, she intends on killing them.