An exciting visit to the Mouse Museum of Natural History turns into a mission when the Trekkers discover that the mouseterious disappearance of bones and artefacts has led to the closing of the Museum. As the Trekkers search for clues, Mo accidentally breaks a bone of a valuable skeleton on display. When Mac mistakenly thinks she broke the bone, Mo faces the choice of letting Mac take the blame or admit his mistake. Mo confesses and the night watchman is so impressed by Mo’s honesty that HE confesses to his sleep walking which leads to the discovery of the missing items and the reopening of the museum.