Having been promised the 'trip' of a lifetime by their Irish friend and mushroom expert Jake, a group of American teenagers arrives in Ireland, keen for adventure.

Despite Jake's warnings about the 'shrooms they shouldn't eat, things start to go horribly wrong and the teenagers suffer horrific visions. The panicked friends are attacked by ghostly creatures, never sure whether they are experiencing gruesome reality or startling hallucinations.

As the group is bloodily whittled down to one, it is soon clear that, whether or not these apparitions are real, the carnage they leave behind certainly is.