After cutting off the blood heart's connection to the bloody network, they went to meet their slaves.
Their slaves were in a room in an inn. They found out what room the four of them were in. Then they entered the room next to it without informing their four slaves of their presence.
After doing this, they activated Life Bond on the Black Knife while being mentally prepared to kill him if he tries to break free from their control.
Life Bond is a process whereby the mark of bondage fuses with the existence of the slave. At this point, the mark of bondage stops being an external object and becomes a part of the slave.
It is because of this fusion that a slave will die if their master dies. Once the mark of bondage fuses with them, they will never be able to escape, and killing them would be as easy as a single thought from their master.
