When the trail starts its long traverse back North to reach the summit of Middle Sister bust straight up on fourth-class terrain, traversing a bit and generally doing the Rockies thing until you're at the base. We got there via a nice left to right slanting ledge with some 5.2 climbing, scramble. The route name pretty much sums the approach up. The first pitch is the crux, thin detached ice to a larger detached pillar. Protection goes in the rock, the pillar is not something you'd want to put gear in.
Pins are useful.
You can do a short third pitch as well and then up the snow to the summit of Big Sister. Cool place, nice views of the Bow Valley. Traverse west along the start ledge until it ends, rap 30 M from a thread with tat, traverse a bit more to the ridge that connects Big and Middle Sister, scramble down this to the trail and walk out in the dark. Fun route, it appeared in late September and was probably better then.