Okay, what just happened? They opened a portal to evil realm? This story is a good and a little predictible but all in all it reads smoothly. I do have a few questions though. What is Shunned House of Lovecraft's? Who is HP Lovecraft? What is a trocar? What is Cthulu? As far as I can tell there are no grammatical errors or spelling errors (that aren't suppose to be there adding the H to W words, interesting.)
A few more details would help in understanding what is going on in the story. The reader has to assume a lot and sometimes when you don't have enough details the person reading gets a little lost.
I like the characters. What were they doing at the house? Why were they at the retreat? Were they taking a break from writing or getting more inspiration, living in the moment? Do the characters understand what happened when the abyss opened up? Why when the candle was kicked over did the evil leave? Why was HP Lovecraft not at his own house? What was with the "Thanks, but we've already got one," at the end?
Keep Writing.