The Voyage of QV66

The Voyage of QV66 is a children's novel by Penelope Lively. It is set in a strange, flooded, somewhat post-apocalyptic England devoid of people, and centres on a group of animals consisting of a dog, a cat, a cow, a horse, a pigeon, and a mysterious character named "Stanley".

Plot
The characters travel in a boat (the titular QV66) with the intention of reaching London Zoo so that they can discover what Stanley is. They have a number of adventures along the way, including being joined by a parrot, several characters losing their way in a balloon, and Stanley himself getting locked in a bank vault. It is eventually revealed that Stanley is a monkey.