About this "The Simpsons" episode:

The Simpsons - Bart of Darkness is the 1st episode of season 6 and number 104 overall in the series.
A heat wave is gripping Springfield and the townspeople attempt to cool down. Bart and Lisa persuade Homer to buy them a swimming pool, which proves popular with the town's other children. Bart ends up breaking his leg when he dives off his treehouse and is forced to spend the rest of the summer in his room. Realizing that he has become isolated, Lisa gives Bart her telescope to cheer him up. Using it, he witnesses Ned Flanders digging a grave and through his ramblings, becomes convinced that Ned has killed his wife Maude. He sends Lisa over to the Flanders' house to look for proof of the "crime", only for Ned to return, holding an axe. However, he is merely putting it away; and it is revealed that Maude is still alive and well, and all that Ned killed was her favorite plant.