"Halloween Who-Dun-It" is the only Halloween special of Davey and Goliath. It originally aired on October 15, 1967.
It is Halloween (or possibly the day before Halloween due to the night being called Mischief Night) in the town where Davey and his dog Goliath live, and there's going to be a Halloween party at town hall that night. Goliath doesn't have a costume yet, and Davey's costume is a secret. Later that night, Davey and Goliath's costumes, as well as Davey's little sister's costume, are revealed. Davey is a spaceman from Mars, Goliath is a dancing tiger, and Davey's sister Sally is dressed as a witch. After meeting Mr. Kloss, who's dressed as a French chef, outside his donut shop, they all head to town hall for the party. Soon, at the party, it's time for the Halloween costume march, a costume contest with six prizes up for grabs.
Davey ends up winning the prize for most original costume, a space missile blaster. Afterwards, it's time to head out. But instead of trick-or-treating, the kids head out and cause trouble, as is expected on this night, which is called Mischief Night by some. And all through the night, the kids refer to themselves by the names of there costumes. And Davey ends up causing some serious trouble, and keeps blaming his costumed identity, "Mars". The next morning, at Mr. Kloss' shop, people are coming in to complain about the mischief from the night before, and he's the one to volunteer and pay for any and all damages.
Meanwhile, over at Davey's home, neither Davey, Goliath, or Sally trust each other after last night's proceedings. Later, Jimmy comes over and explains what Mr. Kloss did, and then sees the problem between Davey and his family. But later, they all realize that they were blaming people that weren't even real, and soon come to the conclusion that they and nobody else caused the distrust between them. Soon, Mr. Green comes over to pick Davey up and take him to the zoo. And right then and there, Davey admits to breaking Mr. Green's beehive the previous night by showing him his helmet from his costume. Then, Davey decides to build Mr. Green a new beehive, to make up for what happened as the special ends.