Webster employs the epistolary structure to good effect; Sallie's choices of what to recount to each of her correspondents reveal a lot about her relationships with them.

As Daddy-Long-Legs traced Judy Abbott's growth from a young girl into an adult, Dear Enemy shows how Sallie McBride grows from a frivolous socialite to a mature woman and an able executive.

Both relationships are affected by Sallie's initial reluctance to commit herself to her job, and by her gradual realization of how happy the work makes her and how incomplete she'd feel without it.

Divorced from her unsuitable husband, Helen ultimately finds happiness in joining Sallie's cause at the orphanage, applying herself to work for the public good.

Socialism applied to charitable causes is an underlying theme; the John Grier Home couldn't survive without the beneficence of the trustees and community.

The novel also deals with the evolving ideas about how best to care for orphans at the turn of the century, with the institution-style establishments falling out of favor, in light of the modern 'cottage' approach.