Your mystic is probably a fraud, I also ran into this event and thought it would be fun to play through using this new feature, but kept failing the last quest. So, I looked at the events, talking to the ghost has a base 40% chance of succeeding and 60% chance of failing and adventuring on your own has a 25% chance of succeeding and 75% chance of failing (with a success modifier of 1.2 for each tier of intrigue: 13, 16, 19, and 22), but if your mystic is a fraud you are virtually guaranteed to fail. Curious, I went and checked my save game file and, sure enough, my mystic was a fraud.
If you want to get past this and win the quest, you can edit an encrypted safe game file, search for your mystic, Cleopatra, and delete the flag 'mystic_is_fraud=<date>'. Of course, if you're going to the trouble of editing a save, you can just add the trait to your character directly.
N.B. There is a base 80% chance a mystic will be a fraud and 20% she won't (modified by a factor of 1.5 at the relevant skill tiers: 10, 13, 16, 19, 22).
