"The Cairn on the Headland" (Howard's third version of Spears of Clontarf) was a horror story set in the present, and succeeded in getting published in Strange Tales (January, 1933).
James O'Brien is an Irish-American researcher who specializes in the history of Medieval Ireland - a subject which he is highly well-informed on and has a passionate feeling of partisanship towards.
The area is shunned by the local citizens, and therefore remains nearly unchanged since the Middle Ages - though the bustle and bright lights of modern Dublin are just around the corner.
The two also argue about the Battle of Clontarf - O'Brien regarding King Brian Boru as not only having freed Ireland from centuries of Viking oppression, but also having saved all of humanity from the occult worship of the Norse deity Odin, whose followers abandoned their ancestral beliefs and eventually embraced the White Christ.
She introduces herself as Meve MacDonnal and gives O'Brien a golden crucifix, decorated with tiny jewels, of an extremely archaic and unmistakably Celtic workmanship.
However, MacDonnal scolds O'Brien for placing a monetary value on the cross and explains she gave it to him as a free gift since he would have need of it - and then she disappears behind an alleyway.
Mistaking the man for a Viking (due to his red hair, unshaven beard, and Norse armor), Odin begged Cumal to provide him with a bundle of holly - the only substance which could restore him to his spirit form.
He arrives at the location just in time to witnesses Ortali uncovering the body of Odin, which remains exactly the same as it was when Red Cumal and his allies built the cairn a thousand years earlier.
Odin immediately reawakens and comes to monstrous life, shedding his human appearance before transforming into "a fiendish spirit of ice, frost, and darkness", with "the shuddering gleams of the aurora playing around his grisly head".
Fortunately, he remembers in time the cross which Meve MacDonnal gave him, holding it high and pointing the relic towards Odin.
As presented here, Clontarf defined not only the future of Ireland but also the fate of the entire world, the whole of humanity - though other Christians in other places failed to appreciate what Brian Boru and his warriors had done for them.
The same point was made by Howard in the related story, The Twilight of the Grey Gods, whose plot all takes place in 1014 and where the participation of Odin in the battle makes it a Wagnerian Götterdämmerung or Ragnarök.
Dorothy Sayers noted the trend of pagan deities sometimes degenerating into Christian demons, as for example the Greek Apollo becoming "The Foul Fiend Apollyon" of The Pilgrim's Progress.