The depiction here is an introduction to the family of Basil Biggs, but at least at this point in time, it is best to think of this family as representative rather than literal. Why?
Basil and his wife, Mary, were from Carroll County, Maryland, and some evidence suggests that Basil’s father was a prominent white slaveholder. Basil and Mary were free in Maryland, and the US Census in 1850 definitively shows them in Carroll County, a thriving agricultural and mill area.

Chapter 2 takes place in 1852; most sources place Basil in Carroll County, Maryland, as late as 1858 with the exception of this discussion of the Matthews Hill settlement placing Biggs and his family south of Gettysburg by the early 1850s. Which is correct? This is nearly impossible to say. Basil and Mary Biggs were illiterate, which was part of the reason for their move to Pennsylvania—they wanted their children to be educated, which was nearly impossible in slaveholding Maryland. Records from the family are unclear.
What is clear, though, is that Basil, his family, and his extended family were ardent abolitionists; in that era, Carroll County, Maryland, was rife with escape attempts, masters advertising rewards for returned slaves, and Underground Railroad connections. This source covers just some of the turmoil in Virginia and Maryland at the time. Basil Biggs and Edward Matthews, another prominent black man on the Underground Railroad near Gettysburg, are thought to be brothers-in-law who knew each other in Carroll County. It’s possible, if not likely, that they had begun Underground Railroad activity in Carroll County.
Meanwhile, Gettysburg and Pennsylvania as a whole roiled with controversy over escaped enslaved persons and the abolitionist movement. Congressman Thaddeus Stevens, who practiced law in Gettysburg for years, helped conduct escapees on the Underground Railroad while also offering legal support to people who became ensnared because of the Fugitive Slave Act. James McAllister, a prominent Gettysburg citizen, founded an anti-slavery society in Adams County more than a decade before the Biggs’s arrival in Gettysburg. The newspapers were full of controversy related to the Fugitive Slave Act, and according to the Adams County Sentinel, a riot occurred in nearby Harrisburg in 1850 over runaways.

The problem with depicting activity on the Underground Railroad in any town in the 1850s is that most conductors and assistants remain unknown. Railroad members scrupulously kept the identities of their associates secret even long after the war. So in the case of Chapter 2, it may not be accurate to have the Biggs family in Gettysburg in 1852, but outside of the Biggs family and a handful of white families, it’s nearly impossible to know who else might have helped in the era. Hence, the “Biggs” family is used to represent the unknown and unheralded people whose names, but not heroism, are lost to history.
For those interested in a firsthand account of the Underground Railroad, William Still’s work might be the best. Still was a major operator of the Railroad and often called the Father of the Underground Railroad. His 1872 work can be read free of charge on Google Books.