The theme of a story is the lesson that can be learned from it and the conflict is the struggle between opposing forces. Usually, one can find a lesson to be learned from the conflict itself or the resolution of that conflict. In Roald Dahl's "The Landlady," the conflict is both man vs. himself and man vs. man, or, in this case, man vs. very creepy old lady who kills handsome young men and stuffs them like trophies.
First, Billy Weaver struggles with himself to make a decision about where to stay for the night when traveling on a business trip. He's on his way to a public inn when he catches sight of an old lady's bed and breakfast. He becomes entranced by green curtains, chrysanthemums, a fire in the hearth, and "a pretty little dachshund" asleep on the carpet. Then, when the landlady tells him about the low price and the breakfast in the morning, he makes the last significant decision he will make in his life. After deciding to stay with the landlady, the conflict shifts from man vs. self to man vs. landlady. Unfortunately, Billy does not discover the landlady's deceitful and murderous secret in time to save his life.
Possible themes associated with the conflict of Billy vs. himself could be the following:
1. Stay on the reliable path (in public places) and don't get distracted by tempting things such as cute little dogs, comfortable furniture, and low prices.
2. Just because something looks nice doesn't mean that it is safe.
3. Things aren't always as they seem.