The Chosen One
Sorry, as the top of this Detective Agency Recruitment board says, You must be subscribed to join/start any agency in Sleuth.
I'm sure someone would be happy to take you on board once your subbed! :)
*Only Subscribers are eligible to join a detective agency*
This is on the message board right above the stickied post that says READ THIS FIRST. In that post the very first thing you will read will be:
At risk of repeating myself:
You cannot form or join ANY agency at all unless you have paid for a game subscription.
In other words, YES, you have to "be subscribed", "buy a membership", "sign up" or whatever other combination of words you would prefer to use to mean "pay money for premium content".
If you read the FAQ at the bottom of every page you will read this:
Do you need to be subscribed to join an agency?
Yes, only subscribers can join an existing agency or create a new one.
So, in other words, no agency, no matter what, can invite an unsubscribed person into their agency. But as Lady Jas says "I'm sure someone would be happy to take you on board once your subbed! :) "