It's been 15 days since Bryan has not washed and the scents he gives off are unbearable! Led by Lisa, the children set up a "commando operation", armed with soaps and shower gels. In the evening in the canteen, everyone is delighted, except Bryan, all clean and hair like a top of the class. At bedtime, Lisa and Matt discover that their bed is occupied by a mysterious guest ... Riton the nutria! Since their friend Bryan has polluted his habitat, he has decided to squat their cabin until his pond is clean!