Errol and Thomas the teddy bear are inseparable friends who play together every day. Errol notices that something is troubling his bear friend. Thomas is concerned that if he confides in Errol he won’t be his friend any more, but Errol reassures him that they will always be friends, no matter what. Thomas bravely explains that he’s a girl, not a boy, teddy, and wants to be called Tilly. Errol hugs his best friend and reassures him that it is his friendship, and not his gender, that is what matters. Errol calls their friend Ava, who breaks off from robot construction to come and play with them. Tilly’s bow tie becomes a hair bow and the three play happily together, having taken Tilly’s identity change completely in their stride, with Tilly encouraging Errol to “wear whatever makes you happy”. The book ends in much the same way as it begun: with the friends enjoying each other’s company just as happily as when Tilly was Thomas.