KABOOM!
Harrowing though the infiltration had been – not only acting the part, but taking the reprimand as the 'failed' squad to return with half their number, and being sent back out again before sun-up as part of another patrol that, for all their sanities, hadn't resulted in them having to kill any halfbreeds – Sarah's team had made it through the night and day to this moment, where the last of the explosives were scheduled to be set and them all exploded. During the hours here while the squads rested – nocturnal by nature or just by necessity, she wasn't really sure, but the Scourge did require sleep and did so in shifts in military-style bunks during the day hours – one by one the team had laid their entrusted explosives in a key spot in the building's structure, until all that was left was the magical ones that weren't so much as set and activated as made and used on the spot.
And now it was time to use them.
After signaling the magical members of the team, of which she was one, Sarah formed the explosives to take care of her designated area, the two large structural supports in the main 'gathering' room, a cavernous space even in relation to the size of the building. Two outwardly-simple crystal balls, like a magic hand grenades, but each with the force of far more, were formed with her will, powered by magic and fed with all her desire to end this threat to the city. Beneath the invisible skin of the illusion, they were only visible to anyone wearing an armband – but not for much longer.
Around them, the squads prepared for the nightly patrols and scheduled slaughters. None of them had noticed anything odd about the defeated squad from last night, not even now as they congregated near a corner of the large rooms in front of the building.
Sarah signaled again, her last act of silence and stealth, and then hurled the crystals at the tall columns. Without waiting to see impact and explosion, she disappeared from her spot and reappeared in the same area the rest of her team had either walked to within the last five minutes, or Apparated/transported to in the last second.
A few moments later, once the buttons on the remotes to the other explosives were pressed, the rest of the shields – magical and more – went into place around the team to protect them from any stray debris from the chain reaction of explosions around the enormous building. After pulling off her armband, thereby ending the illusion so they would not be mistaken for Scourge, Sarah flattened herself against the wall, currently unobstructed by magic, and activated the comm link to let the others know it was now or never.