Don't Call Me Grumpycorn! (PB), Paperback/Sarah McIntyre

Unicorn and his friends are ready for an adventure, and nothing is more adventurous than travelling into SPACE! But when the four friends disagree over which planet to visit first, Unicorn decides to go off alone. Will Unicorn realise that friendship is what makes everything fun? And will he finally stop being such a Grumpycorn?