Ned is with the twins at the mall to see Santa at the Christmas Village when they run into all of their friends. He buys them all popsicles and lets them hang out before they meet Santa. While Jessica has a long list of things that she wants, Liz just hopes that the Super Snooper Club gets a new mystery. Ned then decides to visit his client, Mr. Fox, in his jewelry store to look for a gift for Alice.
While they are looking at all the expensive jewelry, two guys come inside. One is a younger guy with dark hair, while the other is an older guy with white hair in a black suit with a red tie. Mr. Fox shows them some diamonds from his safe, gets distracted, and suddenly realizes that the diamonds are gone at the same time that the two guys take off. Jessica tells security that she saw them steal the diamonds, even though she didn't actually see anything.
The guards give chase and catch the younger guy who lets them check out his briefcase. When they don't find anything, they let him go and warn the twins not to make up stories. Winston then literally stumbles across one of the diamonds in the fake snow at the village. Mr. Doyle, the older man, shows up and claims that it's his. Jessica once again tells the cops that he's a thief, and they once again tell her to stop making up stories and let him go.
The Super Snoopers then decided to spend the day following Mr. Doyle to catch him. Eva pretends that he's a mean old man who stole the present she got for her mother. Some people who work in the shop open up his bags and find nothing, so they tell her to be more careful because she accuses anyone of anything. Winston also trips him, and the twins run off with his car keys, which leads to a massive chase through the mall.
All the kids head back to the Christmas Village and tell Santa that they're his new elves. He lets them dress up and help, but then Mr. Doyle shows up and demands his car keys, saying that Jessica is his granddaughter and she's playing a trick on him. While Santa tries to figure out what to do, Liz sneaks out and finds the missing diamonds in the holiday display. Though Mr. Doyle once again tries to get away, security gets there first. Mr. Fox proves that they're his diamonds, they call the police on Mr. Doyle, and the whole club gets special crystal ornaments for their hard work.
*I'm so confused about what everyone's doing at the mall! It makes it seem like Ned offered to bring the whole group, but then he totally walks away with the twins and leaves them all there alone.
*Ned also offers to get the whole group ice cream and then comes back with popciscles. I hate to be a stickler, but that is not ice cream. Forgive me though, I'm irritated that the soft serve machine at Burger King was down tonight!
*Lila gets all excited at the end because Mr. Fox says he'll give them something from his shop and she assumes that he means they can have anything they want.
*Who the hell takes out expensive diamonds and just leaves them on the counter? Is this the first time they left him alone in the store?
*Mr. Fox claims that he'll be ruined if he doesn't get the diamonds back, and the book says million-dollar diamonds. It's actually just five diamonds in total though. How much could that possibly be worth?
*Ned agrees to let the twins go shopping in the bookstore alone for an hour. What kind of parent lets kids in second grade go shopping on their own in a busy mall?
*He also takes them to the jewelry store and spends way too much time looking at stuff before deciding that he'll come back later. I'm sure that's just what a shop wants during the busy holiday season: someone to waste time and then not buy anything!