Michael Wilhelm approached the Lone Gunmen for their help in finding the Poisoner of Alsace, who he claimed had murdered his father, the prefect of Verzenay. He pushed Frohike to pose as the long lost son of the Poisoner due to how much he looked like the Nazi officer who fathered the boy. He directed them to the woman he suspected, Anna Haag.
Yves Adele Harlow got involved after Wilhelm's recruitment of the Lone Gunmen, since she suspected the man's true identity. Given that the prefect was childless, Harlow believed Michael Wilhelm was the actual son of the Poisoner of Alsace. He was also a member of the East German secret police so he was using the Lone Gunmen to test if his long lost mother seeking him out was a trap set up to capture him.
His plan was to eventually kill the Lone Gunmen but Harlow tranquilized him to collect the $1 Million Dollar bounty on his head.