The arrival of Anne's 14th birthday indicates that almost a year has passed since the family entered the annexe, and a full year since she started her diary. She writes passionately of the changes that are happening "both on the outside of my body and the inside" but admittance to adulthood usually means a few crossed wires with parents, and those teenage problems are multiplied many-fold when you have to live on top of them 24x7.

As Peter and Anne begin spending more and more time alone together in the attic, their initial tentative flirtations soon give way to deeper feelings as each seeks refuge from the frustrations of living cooped up with their parents and being unable to engage in normal teenage activities.

Mrs van Daan is the first to notice what's going on and her natural inclination is to tease the youngsters, but Edith is more concerned. Knowing how easily bored Anne is with new things, she worries that Anne will not realise how easy it will be for her to truly hurt Peter. She warns Anne not to play with Peter's affections, but of course this only leads to more tension between mother and daughter.

For once, it seems Anne cannot rely on her father Otto for support. He too is concerned, although in his case it's more about the unusual situation they are all living in, and what the potential fall-out will be for everyone else when Anne and Peter eventually split. Anne writes a bitter letter to her father telling him she doesn't want him interfering in her life, which greatly upsets the kind and sensitive man.

With the tension built to breaking point, Anne flees to the attic and into the arms of the waiting Peter.