The Zhentarim Mercenaries

Background
The Zhentarim Mercenaries (Also known as the Black Network) were a shady organisation bent on profiting through dark dealings. One of they're main tactics was to take over towns, placing false mayors and lords within towns, and secretly controlling the towns to become a network of sorts across all of Faerun. They held great power during the time of Mystic Obscura, having many towns and cities under their power. They held rivalries with both the Lords Alliance and The Harpers.

Interactions With Mystic Obscura
When Mystic Obscura saved the town of Nightstone from goblins, they found one of the Mercenaries; Kella, hidden in the inn. She feigned she was a traveler, and the group told her to stay put while they looked for Lady Eloithe's cousin.

Another member of the Zhentarim Assassins, along with a special unit known as The Seven Snakes, arrived to take over the town while it was abandoned. The group were refused entry by Mystic Obscura, but were let in by Kella once Mystic Obscura continued their search for Lady Elizabeth Nandar.

The two groups eventually ended up fighting, with Mystic Obscura coming out on top, slaying the groups and saving Nightstone.

Months later, Mystic Obscura heard of the groups dealing with Giants up near Nesme, in the ruins. They vowed to head up there, finding out what was happening.

Not too long after, Mystic Obscura were travelling along the road to Everlund when they met up with another travelling group of Mercenaries. Lady Eloithe spotted their symbol to be that of the Zhentarim, and informed the group. Doing some digging, the group found out that they were taking weapons up to one of their base of operations near Everlund. Deciding not to attack, Mystic Obscura decided to instead take the information up to Everlund, and inform The Harpers.

At some point, The Zhentarim had made a deal with The Harpers to stop the Giants, only to double cross them and make a deal with The Giants to take down The Harpers.

The Zhentarim also controlled the city of Loudwater, even the Lord there was a member of them, and had recently also taken over the city of Yartar, something which displeased Xanathar all the way in Waterdeep.

Mystic Obscura discovered one of their war camps within the North, near the town of Nesme. They managed to skirt it's borders, despite the group seeing the Zhentarim were definitely meeting with the Fire Giant commander.

One of there members eventually became Lord of Triboar, but revealed he was not part of the group who were involved with the Giants, instead wanting to keep himself to the more important business aspects.

Notable Members
Kella

Zalkin

Bases Of Operation
Olostin's Hold

Nesme