The lich spares a few moments from his research and wonders what the intruders are doing. Now that they have spot memorized on the surface near the river, it is easy for Baskiador to come up and check things out. He plans his excursion for some time and picks spells appropriate.
 

• Detect Magic x2
• Spider Climb
• Ray of Fatigue
• Unseen Servant

• Invisibility x2
• Cats Grace * (+4 to dex)
• Sense Shifting
• Spectral Hand

• Fly
• Item
• Spirit Armor *
• Vampiric Touch
• Wall of Water

• Dimension Door x2
• Divination Enhancement
• Wall of Fire

• Monster Summoning 3
• Conjure Water Elemental
• Mordenkainen's Private Sanctum
• Teleport

His objective will be to find out what preperations the party is performing. He will fly over invisibile and check on the troops, the militia, the followers and the townspeople.
He will attempt to find out what members of Local 509 are doing. If he finds easy prey, he will kill with Shocking Grasp or Spectral Hand and take the body back with him to interrogate.
He will make every possible effort to avoid being seen and will not go inside the buildings. However, he can deduce much about the goings on.