Rachel Mackay, usually know as Rachel, is the main antagonist from the book Shadow of the Gallows by Terry Deary. She is a daughter of Lord Arthur Mackay, a former British army colonel, and of Ethel Mackay, a judge. Her half-brother is Bairn, son of Ethel and Bill Twist. Rachel lives in Edinburgh, Scotland with her family. In the book, mother and daughter together prepare the plan to kill Bairn and his stepmother Kitty Bruce by the legal abuse.
Rachel is born in India. Ten years later, she and her family return back to Edinburgh. However, her mother Ethel has also another child, Bairn, with Bill Twist who is an antiquities dealer. No one else knows it, only Kitty, Bairn's stepmother, who visits and threatens Ethel that she will tell her husband about Bairn. Angry Ethel then makes a great plan to kill Bairn, with Rachel in the main role.
Ethel sends Rachel, masked as a young servant with a hat, with a request to a chimney-sweep Bairn is working to. Bairn is send to clean the chimney from inside, although it is forbidden, in Mackay's house. Rachel is "incidentally" siting in the living room that time and when she sees Bairn, she "saves" him and earns a job for him in Twist's antique store.
Later, Rachel appears again as young servant and brings a request to Twist to rob a random house. Bairn is send to this house through the chimney to steal some things. Rachel watches him and then runs to police. Meanwhile in the house, Bairn secretly listens to the plan of three Fenians who are planning to kill Queen Victoria during her visit in Edinburgh. Unfortunately, when the police arrives and Bairn is revealed, one of the Fenians hit his head, so he forgets everything he heard.
He is arrested and Ethel sentences him and also Kitty, who is accused of killing children, to death by hanging. They are then taken to Edinburgh Castle. Rachel, "unhappy" from his fate, accompanies Bairn and "cares about him", but he doesn't know who she really is. She is a really good actress and even cries for "the poor boy".
Rachel later visits Joseph Bell, Queen Victoria's personal surgeon, who tries to prove the innocence of Bairn and Kitty. She firstly tries to drug him, but he doesn't drink his tea and go walking through the city to find answers. Rachel accompanies him and pretends to help him, but she is actually coning and misleading him. She even tells him that she saw a strange-looking young servant with a hat and cruel smile. Luckily, Bell reveals her plans soon.
Thanks Bell, Bairn and Rachel later escape from the castle and even stop the Fenians, as Bairn remembers the night again. Unfortunately, they are arrested again and Ethel is going to sentence them to death, but Bell stops her. He tells the whole story of Ethel, Rachel and their evil plan. He also reveals Bairn who his real parents are. At the end, Ethel is sent to Australia for fourteen years and Rachel for seven years.
Seven years later, Rachel returns back to Scotland. There is a young man in the harbor, waiting for her. It is Bairn who forgave her. The siblings then start to live together and work in Twist's store.