A Lark's Tale

Verity Lark knows everything.
As the London Daily Gazette's popular gossip columnist, she is extremely adept at sneaking into houses, assuming disguises and overseeing a vast network of spies to ensure she stays abreast of the beau monde's comings and goings. If it sometimes seems as though she was hiding behind the settee during a particularly fierce quarrel between a husband and his wife, it's most likely because she was hiding behind the settee during their fierce quarrel.
But nobody knows her.
Writing under a pen name, Verity safeguards her anonymity via an elaborately constructed alter ego. Seemingly everywhere, Mr. Twaddle-Thum is in fact nowhere. He has never met with an informant or skulked in a dark alley. He simply does not exist. That is why she is so startled to discover he has recently been spotted at a variety of locations. A Twaddle-Sham is knocking about London and in such a ham-handed manner he is inciting people to murder.
At least that's what Verity thinks is happening when she stumbles across a plot to kill him.
Or her.
Who is the real target?
Well, see, that's just the problem because Verity can't actually say.
For the first time in years, she isn't sure of anything.