Manannán wrapped his island in mist to hide it from invaders. The Traditionary Ballad records the method: "It was not with his sword he kept it, neither with arrows or bow, but when he would see ships sailing, he would cover it round with a fog." The Supposed True Chronicle adds that he "kept, by necromancy, the Land of Man under mists," and that if he feared an enemy, "he would of one man cause to seem an hundred, and that by art magic."

The Manx Gaelic word for this power is cloagey druiaght — the invisible cloak, rendering invisible at pleasure the person who wore it. Roeder recorded the term in 1904, sitting in a list alongside fer obbah, pishag, and guesag — the wider Manx magical vocabulary still in living use at the turn of the twentieth century. It is not borrowed from the Irish féth fíada tradition. It is a Manx word for a Manx concept.

In Irish mythology the cloak does more than hide islands. In the Wasting Sickness of Cúchulainn, Manannán arrives in a magic mist, takes his wife Fand back from the Ulster hero, and shakes his cloak between them so they can never meet again. Cúchulainn takes a draught of forgetfulness. The cloak separates lovers and erases memory. That is a different kind of power from the one the Manx stories describe, and rather less comfortable.

Whether anyone still believed in the mist by the eighteenth century is another question, but the old sense persisted that the Island was a place apart, sheltered, hidden, answerable to its own customs. Hall, writing in the 1880s, put it simply: "The mists of Little Mannanan, son of Lear, did not forsake our island when Saint Patrick swept him out of it. They continued to come up from the south, and to conspire with the rapid currents from the north to drive ships on to our rocks." The mist outlasted the god. Or the god outlasted the saint.