You didn't see this but I just injected your friend with a deadly dose of insulin.
please just hand it over!
Rory walks into the dark basement with intentions to find the Ripper, and she succeeds. Rory asks why he would kill, and the ripper explained with his backstory. Soon he gets impatient and demands the others to show themselves.
Both Callum and Stephen do as he asks, but because of the darkness no one knew that Stephen was injected with a lethal dose of insulin. The only way that the Ripper would give away the antidote was if they gave away their only weapon, the terminus.
Both Callum and Rory gave away their terminuses to the Ripper. This did get them the antidote, however, it did not stop him from keeping Rory hostage.