I hate how people find Agatha Christie merely a "cozy" writer which sometimes gives off the impression that Christie's books are soft, fuzzy, and cute like what you see in many modern mysteries today that is under the cozy label, and rightfully so too. But The Pale Horse and even Endless Night, two books in the latter half of her career are not cozy. What's so cozy about two girls in a fight and one girl pulling the other's hair from her scalp? That's right out of The Pale Horse. Christie didn't need to make her books graphic and have them soaked with blood in order to have a dark tone. She could be just as dark and create a psychological story just as many modern mystery writers today, including the late Ruth Rendell with her psychological mysteries under the pseudonym Barbara Vine. If Christie lived longer throughout the 70s and into the 80s, perhaps she might have written more books in the vein of The Pale Horse and Endless Night. I also love how in The Pale Horse, she takes characters from other stories and has them make their own appearance, without Poirot or Miss Marple. This makes the characters feel more real and creates as you said a more coherent and cohesive world of her own. It makes her books even more exciting to read as we come across a character from another book and we guess which one that character appeared in.