What is a good thesis statement for The Strange Case of Dr. Jekyll and Mr. Hyde?
A thesis statement needs to state an opinion: it needs to be arguable. Therefore, you wouldn't want to say that The Strange Case of Dr. Jekyll and Mr. Hyde is about a man who splits himself into two people or that it is set in London. These are facts that nobody can dispute.
A thesis statement also needs to be specific. Saying that Dr. Jekyll and Mr. Hyde is about evil maybe arguable, but it is too broad. A thesis statement also needs to be supportable: whatever it asserts has to be supported by quotes and events from the text.
With these ideas in mind, we can move to the novel. What message or messages is it trying to convey? An idea might be as follows: Dr. Jekyll believes that if he could separate out his evil desires and impulses, life would become more "bearable." Yet when he creates his Mr. Hyde or evil self, this evil person feels
younger, lighter, happier in body; within I was conscious of a heady recklessness ... an unknown but not an innocent freedom of the soul.
A thesis statement could argue that it is dangerous to try to become a wholly good person, because when we try to cut out or repress our evil impulses, they come back in a stronger way to haunt us, as Mr. Hyde does when he does terrible things that trouble Dr. Jekyll.
A thesis statement might say something like the following.
The Strange Case of Dr. Jekyll and Mr. Hyde shows that when our evil desires are separated from our consciences, these desires grow stronger and more dangerous.
You might then give examples showing that Mr. Hyde acts badly and that Dr. Jekyll is less free of his evil side than ever. Or you might want to think about the idea that evil is a very strong impulse and what the story is saying about this. Can humans ever escape evil? Is it better to try to integrate it?