There needs (wants, wishes, begs Lol) to be away to become a shadow Druid initiate like you can be come a zhentarim recruit if you are a Rogue.

Convince the zhent agent, after the gnoll fight, to let you have the chest and split the loot with him after you sale it I in Baulders Gate. Once you find the zhent hideout, he will be tied up for treason. After a few dice rolls and a sharp blade (if successful), you are now to deliver the unopened chest to BG as a recruit. It is a bit buggy, so save before you enter the hideout.

My suggestion to trigger the Shadow Druid’s trust is to (as a Druid) allow one of their ranks to “see” you in the swamp getting their info. Allow/help Kagha seal the the grove while NEVER revealing their plans. This does two things

1, This allows their plans come to pass
2, It shows them that you may be of like mind. To get an invite to their ranks, you have to show similar views. Even if you agree with Kahga after you expose them, you show a trait that does not lend to their secretive style and are thus not compatible. And they should attach, like they do.

The Druid that”saw” you can come later with the invite. If you decline you are attacked on-site, by a high level Druid/s, as you can now be a liability…