How do i solve Jans side quest?. Where is the antidote for the poison.

She's not poisoned, but anyway. Lade Jysstev in the government district will tell you about 'the Hidden', and arrange for you to meet with him. He's in the sewers underneath the Copper Coronet - when you get up to the flowing water with the 'bridge', go south. He'll send you on a little wild goose chase to kill some people he doesn't like. When you get back he'll give you his thanks. Go back to Jan's estate and his sister will be healed.