The module was in Dragon #100, and was known as The Mace of St. Cuthbert.
I played Edena in that module. At that time, my oldest character (Edena) was a 9th level cleric.
We had a player character FROM Earth in the company.
So when Edena water-walked his way off the island in the middle of one of London's parks, that character made the ultimate protest: There is only one person who can do that!!
We got to see Dr. Who leave in his time machine.
We did NOT find copies of the Advanced Dungeons and Dragons Player's Handbook or Dungeon Master Guide.
We also did not find the Mace of St. Cuthbert.
We tried again, with Edena and some different characters.
This time, one of our group (he was very high level and had powerful magical armor) decided to take on the English SWAT team.
He died (machine guns are harmful to your health.)
Edena broke into the morgue and threw Raise Dead on the fellow right there. Fortunately, the mortician was not around at the time ...
Again, we did not find the Mace of St. Cuthbert.
Edena tried a third time.
By this time, Edena had become accustomed to 20th century Earth, and somewhat acquainted with the modern concepts of this world.
Unfortunately, Edena was NOT acquainted with the Minions of Cthulu, and had the misfortune to make said acquaintances here and now.
His sanity survived (at least, he thinks it did.) He survived. He even managed to adapt to looking at them and not having his brains run out his ears from the sight (literally.) He had quite a number of nasty battles with these Elder Beings, before fleeing back to Alp Centaur.
And we STILL were unable to retrieve that stupid mace.