Two panels by Hieronymus Bosch entered the collections of the Museum Boymans-van Beuningen in Rotterdam in 1941. They were originally the wings of a triptych whose centre panel has been lost. The wings themselves are incomplete, and are painted recto-verso in an unusual form of grisaille. Apart from one scene, The Departure from the Ark, the iconography of the panels has never been fully resolved, especially that of the four medallions found on the reverse side. This article examines the earlier research and attempts to propose a new interpretation. Drawing on a wide range of comparative works, both from the Bosch corpus and from the artistic tradition within which he was working, the author examines the wings in the light of various biblical sources and their Christian exegesis. This allows for a new interpretation and reconstruction of the damaged triptych: it is a work whose iconography is dominated by the parallel Deluge/Last Judgement. On the two inner faces of the two wings of the triptych we see The Fall of the Angels during the first days of the Creation, and The Departure from the Ark after the destruction of early society. Thus the central panel would have shown the corruption of Mankind before the Deluge, a mankind unaware in its excesses of the punishment awaiting it. On the reverse, the medallions illustrate the trials and the recovery of Job, seen as a model of resistance in the face of evil and a prophet of the Resurrection. Thus is developed a coherent iconographical programme which, balanced between Fall and Salvation, should allow the Triptych of the Deluge to reclaim its rightful place beside the great eschatological Triptychs of Bosch.