Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
Wilcoxes vs. Schlegels: round one.
The tension between the two families begins right away, with Helen's brief and dramatic affair with Paul. Immediately, we see the Wilcoxes and Schlegels in conflict with each other – they're basically polar opposites, which makes them both attractive to one another, and repellent.
Conflict
Mrs. Wilcox leaves Howards End to Margaret.
Mrs. Wilcox and Margaret become friends, and the former tragically dies before their friendship can really flourish. In a seemingly inexplicable turn of events, though, Mrs. Wilcox leaves Howards End to Margaret, which puzzles and angers her husband and children. The Wilcoxes choose not to tell Margaret about this bequest, but it still sets up a sense of suspicion and fear with regard to the Schlegels, especially in Charles.
Complication
Henry and Margaret get married.
Despite their odd and complicated history, Henry is drawn to Margaret, and she to him. They decide to marry, which throws everyone into a tizzy – nobody else is pleased about this. Helen and Charles are especially unpleased. We can't tell how this is going to pan out; how can the Wilcoxes and Schlegels possibly interact as one single family?
Climax
Evie's wedding brings Helen back, with the Basts in tow.
All of the Wilcox-Schlegel tensions come to a head at Evie's wedding at Oniton Grange. Helen unexpectedly shows up with two unwanted guests, Jacky and Leonard, saying that they're starving and it's the Schlegel's fault. What she really means is that it's Henry's fault, since he gave the fatal advice to leave the Porphyrion anyway. It's revealed that that's not the only thing to blame Henry for – he also had a torrid affair with Jacky ten years ago, which may or may not have been the cause of his ruin.
Suspense
Helen is missing in action; everyone wonders if she's OK.
After the debacle at Evie's wedding, Helen goes off the map for a while. She doesn't want to see anyone in her family, and it seems like she's left England forever. Nobody can understand why – Margaret thinks that it's because she hates Henry so much, but that just doesn't seem like a satisfactory explanation.
Denouement
Helen is tricked into coming to Howards End, and her pregnancy is revealed.
Finally, we understand what Helen's been up to. The fact that she's pregnant makes everything fall into line, in a tragic way; all of the characters are brought back together a final time, in which the conflicts (Wilcox-Schlegel, Schlegel-Bast, and Wilcox-Bast) are all out in the open. Poor Leonard bears the brunt of it, and is killed as a result. However, though this isn't a happy unraveling of conflicts, it does allow for the whole world as we know it to be reevaluated.
Conclusion
In the aftermath of Leonard's death, a new order is established.
The fallout of Leonard's death by Charles's hand creates a new world for the Wilcoxes and Schlegels. Howards End ultimately ends up as their new home, and at the end, we see all of the loose ends tied up: the Wilcox children end up with all of the family money, while Margaret, Helen, and Helen's baby end up with the house.