After Save Point 1 - Getting that darn purple key

[otg]

Lara wrote:
Anyhow, I got my yellow key and went upstairs towards the grey room start point (16499). But in the room to the left of that is the room with the lever, three grey doors and the purple key. How do I get the purple key? I can't see anything hidden that would enable me to get open the grey door at the top of the ladder wihtout 'actioning' the lever below. Then I can't get back!

Help?
.

I just played it to the first saving point [which has two pedestals... probably for a good reason?] and went up for the purple key. I get a feeling that the idea is to go not back, but forth, the same way, do a second save [so you don't have to do it again] and enter the room with the purple key again, this time with the grey door open! tadaa [haven't got the purple yet, just the second save... but now: off to the dungeon!]