|Relationships|| Mycroft Grimesby (twin brother)|
Roderick Grimesby (father)
They are born into a poor family without the means to support two children. Roderick and his wife kept Harcourt and gave up Mycroft.
The remains of Harcourt's 10 year old body is discovered at the bottom of the armoire at the end of the episode.
Since Mycroft, pretending to be Harcourt, told Murdoch a family tale that fit the evidence, he is released when he tells Detective William Murdoch that his twin brother, thought to be alive, had murdered their father. By the time Murdoch uncovers Harcourt's body, Mycroft is untraceable. While it is clear that Mycroft killed his father, it is ambiguous who and how young Harcourt died and how their deceased mother died as well.
The Grimesby men had the genetic trait known as heterochromia in which the eyes are different in colour. Where Roderick and Harcourt had brown left eyes and blue right eyes, Mycroft had the reverse. His puppet was painted similarly. This fact would have given away which twin was which to their parents.