Anna Haag was a woman from Alsace-Lorraine who wanted to find her long lost son. She ran newspaper ads in Europe trying to locate him. She was suspected of being Madame Helena Davos, the Poisoner of Alsace.
As Frohike went undercover as her son to confirm this, he came to realize that she was no killer. Her personality wasn't entirely friendly but very kindly under the surface. She was just another person destroyed and strengthened by War's doubled edged sword.
She helped the Lone Gunmen and their associates, Yves Adele Harlow and Jimmy Bond, pull off the trick that led the real Madame Davos, Louella Everage, to reveal herself to the wake of Mrs. Allsop.
In the end, Frohike apologizes for all that he did in pretending to be her son but Anna Haag tells him that for one day she knew what it was to have her son back.