Postmark Murder — Mignon G. Eberhart

The little Polish girl with frightened eyes is, as far as Laura March knows, the only living blood relative of late Chicago businessman Conrad Stanley. Found in a European orphanage, Jonny Stanislowski has been flown to America to inherit her share of Stanley's fortune along with Laura, Stanley's ward; Doris, the young wife of his May-December marriage; and Charlie Stedman, his business partner. Having grown up an orphan herself, Laura feels compelled to befriend this fearful child who speaks no English--a decision that will entangle her in murder.

Within days a man claiming to be the girl's father shows up at Laura's apartment. Later a mysterious phone call sends her to a seedy boardinghouse...to find his corpse. All the heirs have a motive to want him dead. But the police choose Laura as their prime suspect! Soon a net of lies and damning evidence is tightening around her...someone may be trying to kidnap Jonny...and Laura's last hope may be a truth locked, deep and dark, in a child's mind.