My thoughts are in blue, words to delete are in red, suggested rephrasing is in orange.

I am seeking representation for THE GRIM UP NORTH, a supernatural detective novel. I advise everyone to open with their hook, and skip anything else. The fact that you're writing to them seeking representation is an assumed.

The dead speak to David Teasdale – in fact, they never shut up.This is a great hook, so you need to put this front and center Ever since his father slit his own throat after stabbing David and killing his brother, David’s heard ghosts. The inciting incident (and obvious trauma included, I'm sure) is a good thing to have here, but this second sentence at the end tells us the same thing that the opening six words do. Also, the slightly jokey voice of they never shut up feels at odds with the very heavy suicide and child murder that follows that up. You'll need to decide what's a better representation of the voice of the book - humor nods, or heavy dark shit - and pare down on the one that doesn't fit best.

Spooks, spectres, phantoms, phantasms, whatever you want to call them, he calls them annoying. For twenty-five years since that night, David has been trying to drown out the spooks’ whining, incessant voices with whatever comes in a bottle and costs less than a fiver – Special Brew, mouthwash, nail polish remover, he’s undiscerning. I think you need to combine these opening two paras, and slim down on the description of the child murder to buy you some more space, and get the setup in the first para, then move us into the actual plot, below

David’s daily routine from his flat to the alley behind the Cash and Carry is disturbed when a spectre claiming to be his brother floats through his door with a warning. Is he an actual detective? Like a PI? Does his ability to hear the dead benefit that? Clarify In five days, a bloodthirsty spirit of vengeance will rip through the streets of Newcastle in search of those that killed him.

To stop an impending massacre and rid himself of his curse Why would stopping the massacre rid him of the curse?, David agrees agrees with who? to hunt and kill the perpetrators What perpetrators? before delivering their souls to hell. But in the course of justice, David will be shot at, stabbed (again), possessed and have his testicles dangled over a meatgrinder in a journey that will take him to hell and back.

It’s at times like these that David remembers what his dad said to him and his brother before he went bonkers: “It’s grim up north, lad.” IDK if you need this last little para. I know it's there to explain the title, but if an agent is interested they will request, title nonwithstanding, and the last line of the previous para is a better ending point

The novel is complete at 88,000 words and combines our love of pavement-hitting gumshoes and all things spooky. THE GRIM UP NORTH contains the nerve-shredding mystery of Stacy Willingham’s ALL THE DANGEROUS THINGS with a twist of the gothic richness of Johnny Compton’s THE SPITE HOUSE.

This is a stand-alone work with the potential to continue David’s journeys into the world beyond.

The idea here is solid and most of it is pretty good, you just need to pare down the first two paras into one and clarify on the points I have questions about.