(I'm posting this summary for a player who missed the game. Sorry about the lack of context for anyone else reading it!)
Xavier had gotten a good look at the 1st and 3rd floors, and a quick glance at the heavily guarded 2nd floor. Given his recommendation, along with Lee who found an air-vehicle hangar on the roof, the team decided to enter from the top. Rugby headed out of town to provide a long-range "shell the ziggurat" distraction if they were made. Akira cast True Invisibility and Exalted Conceal Arcana on everyone in the group (for -6 to further Spellcasting rolls!) and amazingly, they were able to fly in on Tiamat without being detected and land (poorly) on the roof.
Xaver opened the hangar roof and Lee took out the guard within. They found a TK Flyer (a mid-sized ornithopter TW vehicle), a closet full of parts (which they loaded into the flyer, with plans to steal it), and a cool astronomical observatory room that Lee rigged to blow up. They headed down to the 2nd floor and were taken aback by the number of guards there, so Ellie teleported everyone directly into what they thought was the main experiment room. It was, but the room also had magic-analyzing runes that alerted the four occupants -- Sir Aloysius Velde, another mystic knight, and two necromancers -- to the teleportation, and they used Exalted Detect Arcana to see the party. A fight ensued in which the party won, using relatively quiet attacks, so while Tiamat held the door, Lee (who'd recorded Sir Velde's voice) was able to impersonate Velde enough to keep the outer guards from entering.
The group looted the bodies and also found a Lightning Rod and Iceblast Shotgun in a supply closet. Then Akira and Xavier double-teamed the arcane lock and got into the deeper ritual room, which had one guard (knocked out by Ellie), a few vampires strapped to upright tables, a bunch of alchemical reagents, and a TW computer mainframe. Akira and Xavier double-teamed the computer to get key info, including how the ritual worked (short version: dose vamp with alchemy, necromancer channels PPE for a ritual, mystic knight rechannels the PPE into the vamp, both now have partial control over the vamp . . . in theory), and that at best they've been able to hold control for a few days, but not reliably.
The team strapped a bag of key reagents to Tiamat, rigged the rest to blow up, and teleported first to the library (where they stole a bunch of books, and Lee rigged yet another grenade to blow) and then to the hangar to steal the TK Flyer (and, yes, rig another freaking grenade trap). With some psychic and magical help from Tiamat, Xavier was able to fly out without attracting attention, and amazingly Akira had kept up both True Invisibility and Exalted Conceal Arcana the entire time, which let the group get away and rendezvous with Rugby.