Grania, the most beautiful woman in Ireland, was the daughter of Cormac MacAirt, the High King of Ireland. She was courted by all, including the now ageing chief Fionn MacCool, who wanted the young maid as his second wife. He asked her to marry him, she agreed, and a great feast was set up to celebrate the newly engaged couple. But on that night Grania met Diarmait, one of Fionn's best warriors and it was love at first sight. Grania was prepared to go to any lengths to get her man and drugged the entire party, apart from Diarmait. With Diarmait all to herself, Grania confessed her love for him, but Diarmait backed off, as he was loyal to his leader Fionn. But Grania wasn't taking no for an answer, so she put a spell on him, and he fell in love with her. The two ran off together, hotly pursued by a very angry Fionn and his men. The eloping couple ran all across Ireland, laying together in caves, trees and all kinds of nooks and crannies. Local legend tells they eventually ended up in county Sligo and resided at Annacoona cave on Benbulben mountain.

After long years on the run, Grania fell pregnant with Diarmait's child, but fate was about to catch up with them. One day out in the wilderness, with Fionn and his men closing in, Diarmait and Grania came across the heath of Benbulben in Co. Sligo, where a giant boar confronted them. This was bad news for Diarmait, whom legend had told that the only living creature that could harm him, was a wild boar. As the boar charged, Diarmait, protecting his heavily pregnant lover, wrestled it to the ground in a fight to the death. The warrior killed the boar with his sword, but not before the boar had gored Diarmait, fatally wounding him.

As Fionn and his men came upon their long-sought quarry, he found Diarmait dying in a heavily pregnant Grania's arms. A despairing Grania knew she had just one chance to save her lover. She implored Fionn to show mercy and save his former friend by curing Diarmait with a drink of water cupped by his magical hands. But Fionn refused, still hurt that his best friend had eloped with his betrothed. With Diarmait dying, Fionn's men begged him to help this once great warrior to live. But still Fionn refused. It was only when Fionn's son Oisin challenged his father and threatened to kill him that Fionn agreed to help Diarmait. But it was too late, Diarmait had died before Fionn could save him. He looked at his dead friend with the life-saving water falling between his fingers. The question remains, what would you do with one last drop?