You're referring to 'Black by Gaslight' by Nene Adams, aren't you? God, I remember reading that series so long ago, but I was enthralled every second of the way. It's nice to meet a fellow fan!

I think Adams still has it 'Black by Gaslight' online at her site though as seen here. I haven't read her published novel of Gaslight, but I'm assuming that there's more scenes within it, no?

It would be an interesting take to have our favorite ladies here follow a similar path of solving mysteries.