Ottoline and Mr Munroe love puzzles, clues and mysteries. One day, they meet an enigmatic purple fox, who offers to take them on a night-time urban safari. The fox shows them all the hidden animals of the city and Ottoline makes notes on them in her field notebook. Mr Munroe is making notes too - on the anonymous poems he finds stuck to lampposts on their journey. Who is the secretive poet, and how can he and Ottoline help them mend their broken heart?