"It didn't look as if he'd touched his costumes." Only a few casual outfits? And a suitcase? Where would he go, if he wasn't planning on working? He wouldn't up and decide to quit supervillainy, so what was he planning to do, and why?

"I assume neither you nor anyone else noticed anyone strange about? Would it be possible to speak to this Alto?" He really is missing, then. The Case of the Missing Meister. Hmm, sounds like Sherlock Holmes mystery... or Nancy Drew.