Complex sentence: Hastings first meets Poirot during his years as a private detective in Europe and almost immediately after they both arrive in England, becomes his lifelong partner and appears in many of the novels and stories.
Split into simpler sentences: Hastings first meets Poirot during his years as a private detective in Europe. Almost immediately after they both arrive in England, he becomes Poirot's partner, and appears in many of the novels and stories.