The Small Family is on a big move from North Carolina to Ohio. The house they were moving into was part of the Underground Railroad and used to belong to a man who went by the name of Dies Drear. Mr. Small, Mrs. Small, Thomas, their eldest son, and his twin brothers, all had different emotions about the house. Thomas had many questions about the house, but his dad kept ignoring his questions. Mrs. Small was trying to lighten the mood and the twins were crying and wouldn't stop.
When Thomas took the twins outside, he found and pressed the button on the doorknob which opened the stairway and revealed a passageway to a tunnel. As the stairway opened, he saw a horse and two strange kids. The kids introduced themselves as Mac and Pesty Darrow. A few minutes later he found himself in the tunnels exploring. He heard an "ahhing" noise before he ended up in the wall of their kitchen.
Later, Thomas was told that the "ahhing" sound came from Mr. Pluto's cave. He was the caretaker of the house and was doing his blacksmith work there. Mr. Pluto was a very odd man. In the night, Thomas had been chased into the house by him. Now the family was starting to feel suspicious. In the middle of the night, Thomas heard a noise. and in the morning, they found three triangles on their bedroom doors. They think Mr. Pluto snuck in and did it.
The Small family went to go find a locksmith. When they found the locksmith they were told more about the Darrows and also their new house. They also found out that there was "bad blood" between the Darrows and Mr. Pluto. Then they took a trip to the college where his father was going to be working at and found the fourth triangle in his classroom and discovered that all four made a Greek cross. When they came home their kitchen was covered in flour and weird goop. They suspected that it was the Darrows.
Thomas and his father went outside to try to figure out who messed up their kitchen and found Mr. Pluto's cave. They met Mr. Pluto's son who looked very much like him. His name was Mayhew. Mayhew went back to their house with them and helped clean up their kitchen that the Darrows destroyed. They had a plan to scare Darrows away so that they would leave Mr. Pluto and the Small's alone.
Mr. Small, Thomas, and Mayhew convinced Pluto to go along with their plan. Three Darrow boys came along to see if anyone was in Mr. Pluto's cavern so they could sneak in. Their plan worked great with Thomas and Mr. Small as the slave ghosts and Mayhew as the white abolitionist, Mr. Pluto was himself, and there was the strange winged horse. The Darrow boys got so scared that they said they wouldn't ever come back. Mr. Pluto, Mayhew and the Smalls all began to trust each other.