The spell was cast before Locke fell more than a few inches - as silent leviosa to control his descent and float him to the ground. Charms weren't Severus' specialty, but the flick and swish had been drilled into his memory by Lily until he'd perfected it. He made sure the man landed on his feet gingerly and released the spell with another flick of the wrist.
He shoved his right hand into his pocket, leaving his wand in his left as he crossed to meet his new and random ally. "What are we dealing with?" he asked, turning his head to nod at the rafters. He thought he saw something that looked like a tentacle, but he wasn't positive. From what he saw, it wasn't anything he recognized.