As was usually the case Charlie was the last out of the club. The last of the other staff had left once the takings were counted and stowed in the safe. Since Gringotts didn't open on a Sunday and he'd need money to make the floats for the various cash drawers Saturday generally wasn't a depositing night. Someone would supervise those being set up the following night so he had a record of it all and the balance could go in the overnight deposit on Sunday.
By the time Charlie had pulled his long coat back on and set the inside wards he expected the street to be empty as it usually was at gone four on a Saturday night or Sunday morning if you preferred. At first he thought the street was empty and began to set the wards, but a noise distracted him. It didn't sound like the expected rats or cats, but a soft sort of thump. He finished the spell he was working on automatically and looked around. He didn't see anybody though and continued with the layers of protection. Then the thump came again and he spun around. That time he spotted the figure over on the far side of the street almost lost in shadows and clothing that blended with them.
"Oi, are you okay?" he called, assuming it was a drunken customer of either his or Seamus' who had got turned around on their way hom.