The Ongoing Campaign

The third segment of my ongoing campaign (quite some time since the last time)

The heroes had just vanquished a bandit camp terrorizing Stonedelve. The only clue they had found was a letter with dates and times stamped with a seal featuring a Red Tower. They continue their march north until they encounter a pregnant woman being plagued by two bandits. Both bandits were wearing an armband with the same Red Tower symbol as the letter that was found. They killed the bandits and save the woman who says her name is Shari. She says she was visiting family nearby and was now on her way back to Underbridge. But our heroes think she's lying, and they will later turn out to be correct. She decides that she will accompany them on the journey north.
Eventually they arrive in Fourstones where people have been going missing. During their stay Mercurios, the elven cartographer disappears. After a frivolous search the heroes find nothing except that men have been seen around the village at night wearing armbands. They depart the now named Four Slightly Smaller Stones to search for clues in the area, leaving Shari waiting in the inn. They eventually end up in Underbridge, without the pregnant Shari.
There they discover a city in trouble. Digger's Pass, invaluable for trade with the rest of Devalon, has been flooded and an emergency city guard has been razed of mercenaries under the command of a merchant named Neil Grater. The baron of Underbridge has taken ill and is no longer leaving his mansion. The son and daughter-in-law of the baron are gone to visit relatives far away, this effectively leaves the city in the hands of the questionable Neil Grater and a small contingent of Red Tower guards sent by the Steward of Devalon. The heroes are convinced of Grater's roll in all of it but cannot prove anything. After they meet him and mention a local inn keeper who has spoken out against him, they find the man's inn burned to the ground. Grater offers them stay at his inn, and showers the female party members with gifts. Unable to enter Grater's mansion or pay a visit to the baron, they decide to explore Digger's Pass. They not only find it trapped but also find Red Tower guards and Grater's sorceror, Gardon running an operation out of an abondonned segment of the tunnel network. They attack Gardon and the guards, capturing Gardon. He confesses that they have been using slaves that they kidnapped from neighboring village to dig in the tunnel in search of a mysterious gem.
They take Gardon to Grater's manion along with all of the slaves they freed and demand he give up. Grater reluctantly agrees and is taken into custody by the real town guards. They reunite the baron with his son and they are handsomely rewarded. The son then leaves after learning that his wife, Shari, is in Fourstones.
Our heroes bid their farewells and set off through Digger's Pass towards Devalon and the insidious Steward. At a brisk pace they arrive quickly at the capital and use the armbands from the captured Red Tower guards to disguise themselves. They report in and convinces the local guards that the bring a message for the Steward. They confront him with all that they have learned and he thanks them for stopping the plot in Underbridge. The Steward reveals that he knows who the adventures are and has heard of their exploits. He know wishes to hire them for a dire mission. He explains that he only sent the Red Tower guard to Underbridge to secure the gem hidden in Digger's Pass and that they misinterpreted his orders. The gem he seeks is one of five gems of power. It is through these gems that the gods manifest their power on the world. These gems have suddenly started evil, corrupting everything around them, including their guardians. The Steward already has one gem, the emerald of Maitri which was secured from a temple near Smallbank. The guardian linked to the gem regenerates daily and to prevent this from happening the emerald is kept in a special box. His only intention is to find the gems and perform the purification ritual. And he asks the heroes if they would find them for him. They agree, but only if they take the emerald of Maitri and all copy's of the book detailing the cleansing ritual. Right before they leave, they promise that after they will come back within two weeks to kill the Steward.

Answered questions:

Why is part of the woods near Treeshine and Stonedelve evil?
What happened to the guardian of the temple of Maitri?
Why did the giant's youths turn into ogres?
What is the mysterious gem and how is it linked to the salamander and the rest of the plot?

New unanswered questions:

What do the new dreams that the party has been having mean?
Why are the gems of power turning evil?
Where are they all hidden?
What is the goal of the Steward, is it as he says or is there more?
How much more is there to the legend of the gems?
Why is it that no one has found the gem in Digger's Pass when the location is so obvious?
What other mysteries does the tunnel network of Digger's Pass hold?
What happened to Grater and his men, is it safe to assume that they are gone for good?