Lola is really, really excited about looking after the school guinea pig, Bert. She can't wait because she has learnt completely everything about guinea pigs – 'Bert is just going to just completely love it'. Lola loves playing with Bert, and she and Charlie even build him his very own guinea-pig run! But when Bert goes missing, Lola soon discovers that she knows something about Bert that no one else has even thought of . . .