In Mother Night by Kurt Vonnegut, the Blue Fairy Godmother, also known as Colonel Frank Wirtanen and Harold J. Sparrow, tends to show up when the protagonist, Howard Campbell, is in a fix. Let's look at this mysterious character in more detail.

Wirtanen is the person who originally recruits Campbell as a spy against the Nazis. Campbell is living in Germany with his German wife, and the couple decides to stay there during World War II. Campbell starts writing propaganda for the Nazis and then becomes a spy. After the war, Campbell returns to the United States before his role as a spy is revealed.

Time passes, and Campbell finds himself in league with some Soviet spies, but he is warned by Wirtanen, again in his “fairy godmother” role. Wirtanen also tries to warn Campbell about a raid, but the latter gets caught in the middle of it.

Campbell ends up turning himself over to the Israeli government to face charges as a Nazi, and Wirtanen is the only one who can vouch for Campbell's role as a spy. Finally, Wirtanen writes a letter to clear Campbell's name, but it does no good. The “fairy godmother” cannot save Campbell in the end. Campbell commits suicide.

You should think about how Wirtanen is a mysterious figure, an ambiguous figure, who symbolizes all the strange happenings and ambiguities in this novel.