“Doctor, here’s a tip: When I’m on a date, when that rare and special thing happens in my real life, do not, do not under any circumstances put the pope in my bedroom!”
The episode begins as Doctor Who meets Umberto Eco/Dan Brown and H.P. Lovecraft/Robert W. Chambers, and for all the talk of mass suicides and death, it’s surprisingly hilarious.
The second half takes a dark turn based on some familiar SF tropes.
We also learn who is in the vault and why the Doctor took his vow.