It's about a family that moves into Keyhouse, a mysterious old mansion. There are magical keys in the house that unlock various powers and secrets. The Locke family has to deal with the strange things related to these keys while also facing some dark forces that are attracted to the keys' powers.
Well, the Locke family forms the core of the main characters. Tyler, being the eldest, has to take on a lot of responsibilities. Kinsey is trying to find her place and has her own growth throughout the story. Bode is the cute yet mischievous youngest. And then there's Rendell Locke, their father, whose past actions and knowledge of the keys also have an impact on the story. Dodge, as the villain, adds the conflict as he constantly tries to outwit the Locke family to get his hands on the keys.
Well, it varies depending on the specific story arcs and editions of the Locke and Key comic. You'd need to do a detailed count while reading to know for sure.