When Sprig’s rare and precious Blue Moon Shell is stolen, he and Anne investigate to find the thief.
One early morning, Anne is greeted by Sprig who has found a blue moon shell which are pretty and rare. Sprig's plan is to give it to Ivy for her birthday. Amazed at the romantic gesture, Anne fully supports it, but Hop Pop arrives to ask the kids to clean Bessie's stable. Sprig chooses to leave the shell out in the open despite Anne's worry that it will get stolen. After they come back from work, the shell is gone, saddening Sprig. Anne suggests that they play cops after showing Sprig a video of a cop show. Impressed by the premise and its intent, Sprig agrees and they start by locating their first clue: a piece of wax string from the Grub & Go.
Sprig and Anne, adorned in mustaches, confront the cashier at the store who does not know anything. Anne, noticing that Sprig is acting too soft, convinces him to get mad for the shell being taken. The cashier states that the string was bought by Chef Flour. They head to the bakery and confront him with Sprig threatening to destroy his favorite apron for names to the people who bought baguettes (the reason for the string). Anne soon becomes worried over Sprig's behavior and soon he uses his angry tactic against the people of Wartwood.
They finally confront Gunther, a kindly new resident, and Sprig once again angrily confronts him by destroying his things. Gunther then reveals that he is a Southern Tusked Frog and begins transforming into a behemoth and chasing Sprig and Anne away. They attempt to get help, but nobody wants to due to Sprig's behavior. Eventually, Sprig confronts Gunther and apologizes, causing him to calm down. They return home defeated only to see that not only is the shell returned, but Ivy was the one who took it as she wanted to clean it. Sprig offers it to her as an early birthday present, but she wants Sprig to keep it so that she know she is close to his house. As she leaves, Sprig tells Anne that Ivy "stole [his] heart", but tells him that it is too much.
- Brenda Song as Anne Boonchuy
- Justin Felbinger as Sprig Plantar
- Bill Farmer as Hop Pop Plantar
- Amanda Leighton as Polly Plantar
- Chris Sullivan as Gunther
- Scott Menville as Quentin
- Kevin Michael Richardson as Chef Flour
- Stephen Root as Mayor Toadstool
- Jack McBrayer as Toadie
- John DiMaggio as Stumpy
- Katie Crown as Ivy Sundew
- The episode's title is a reference to the novel Crime and Punishment.
- Gunther is similar to the Incredible Hulk in that he gets angry and transforms into a giant frog.
- Southern Tusked Frogs are actually found in Australia, yet Gunther speaks with a stereotypical southern accent that sounds similar to Kermit the Frog.