This paper examines Michelangelo's unfinished Florentine Pietà and the part played by Tiberio Calcagni in its 'completion'. The essay first considers the ambition and technical difficulty of carving a marble group of four figures, which may partly explain Michelangelo's abandonment of the work. Secondly, new documents provide a fuller picture of Michelangelo's long-time friend and assistant, Tiberio Calcagni. Calcagni's relations with Michelangelo are discussed, as is his critical role in saving the damaged sculpture. Finally, the essay considers the anomalous inclusion of the Mary Magdalene and her importance for the composition and iconography of the sculpture.