Landmine in Neutral Grounds Casefile - need clarification

[kittiehawk]

Hello!  I ran the Neutral Grounds Casefile for a group this weekend, it was my first time as GM so we spent a lot of time hashing out how certain rules worked.

We had an issue with the landmine encountered in Act 2.  Here is how it is described in the file:

He’s surrounded by a hemispherical “land mine” type ward—it’s a 6 shift ward that, if tripped, explodes into a 4-shift attack (yes, that’s a +4 attack at Weapon:4) on everyone in the room, including Frank.

I took this to mean that I would roll, modify it with the 4-shift power of the attack, compare with the players defence and then add the weapon:4 to determine the number of shifts the players would take if the attack succeeded.   My players rolled pretty badly, resulting in 10 shift attacks on two of them and 8 shift attacks on the rest.  It seemed a bit extreme for that early in the game, so I ended up reducing the damage since I didn't want to cripple them going into the last act.

Was that the correct way of calculating damage for a landmine type ward? 
Should I even be rolling for the attack, since as it is a thaumaturgy effect, it has a set amount of power in it?  Or would they just roll their defence versus the +4 attack?

Thanks for your help! 

At least they're going to be a bit more cautious when investigating from now on.   

[narphoenix]

It has a set amount of power going in. You roll defense against a Great attack. Unless you roll defense into the negatives, there should be no conceivable way to take 10 shifts of damage.

[kittiehawk]

I thought that must have been my mistake. They refer to the effect of a landmine to be similar to evocation, so I thought I had to roll it as an attack with a +4 modifier and then add the weapon damage.

Thanks for the clarification!

[terrics]

I am really glad you asked that question. I will be using the Neutral Grounds Casefile to run my first Dresden Files game and would have had the same question. Did you have any other lessons learned from this one? I'm curious - how much time did it take to go through the group character work? I'm used to D&D and WoD, so this approach to character creation is definitely different.