CSI Mossy is the sixth episode of Shaun the Sheep: Adventures from Mossy Bottom.
Shaun and Bitzer hunt for a whistle thief on the farm.
In the evening, Bitzer is enjoying blowing his whistle, which disturbs a hen, Timmy, a pig, and Stash, much to their dismay. After an evening of whistle-blowing, with one last blow that annoys the same hen, Bitzer then goes to sleep.
The next morning, every animal in the farm notices Bitzer's panic. Upon knowing that Bitzer is missing his whistle, many animals are enjoying the dog's mishap. Bitzer immediately interrogates the animals who mock his plight the most, to which Shaun stops him from continuing. Knowing more of Bitzer's distress, Shaun starts inspecting and collecting clues around Bitzer's dog house. With every evidence gathered, Shaun and Bitzer start their interrogation.
At night, Shaun gathers nearby animals who are suspected to have stolen Bitzer's whistle.
First, Shaun accuses Timmy with the clue of a footstep of the lamb's size. However, Timmy then explains that he was merely searching for his football at night, which went into Bitzer's house. This causes Timmy's mother to chastise Shaun for blaming her son. Shaun gets embarrassed of his mistake afterward.
Next, Shaun accuses Stash with the clue of acorn leftovers. Immediately, Stash explains she had put down her acorn collection last night to use Bitzer's toilet, which explain the leftovers. Shaun gets embarrassed again upon being wrong.
Then, Shaun accuses the hen with the clue of a chicken feather. Shocked, the hen explains that she used a hairdryer last night, which blew her feathers as far as to Bitzer's house. Embarrassed, Shaun leaves to find any clues.
Finally, Shaun accuses a pig with the clue of a fly. However, the pig then accuses the other pig, who pelts his food at Shaun. Immediately, things escalate into a brawl as Bitzer suddenly grabs his whistle from his hat and blows it to stop the fighting.
Bitzer is then joyous to have found his whistle, only to realize the other animals aren't as happy as they've been through a lot of trouble to realize Bitzer's the one who's been keeping the whistle. As Bitzer escapes from others' wrath, Shaun photos the dog and puts it on a board, humorously claiming Bitzer is the true suspect of the crime.