There is something that has confused me for some time concerning multiple investigators in a Vignette. Here is a situation, a paragraph requires the Team Leader to make a Will +0 check or go Insane, drop to 1 Sanity and move immediately to Arkham Asylum. Does this happen to all Team Members or just the Team Leader? Or a second example, would all Team Members suffer being Lost in Time and Space due to a failed roll by the Team Leader?

A side question also is: I have always disliked Assisted Skill Checks and the Team
Leader. The rules states:

"Some encounters call for “assisted” skill checks. These are normal skill checks except that before rolling an assisted skill check, the team leader may offer for another team member to take over as team leader, so that another investigator is making the roll (and becomes team leader)."

However, the ability to switch Team Leaders right before a roll seems to negate the function of a Team Leader. I have been playing with a house rule that the current Team Leader remains for the turn, and that other Team Members can only conduct Assisted SKill Checks per the normal rule.

The team leader makes all skill checks and takes all risks and rewards that result. If there is damage taken or some other negative effect, then the team leader suffers the damage. If there is a reward, the leader decides who gets to take it or how it gets divided up. (Of course, the case book writer can override this whenever it makes sense.)

The investigator that makes an assisted check becomes the new leader precisely because of the above rule. This second player is taking the risk of making the check, so they must also deal with the consequences (good or bad).

Perhaps you are getting too hung up on the word "leader." You can think of the team leader as whoever is leading the discussion at any particular moment. Suppose a team is breaking into the cult stronghold. They get to a locked door, and the so the investigator with the highest sneak says "Hey, I know how to pick these locks. I used to do it for fun when I was a kid. We'd break into the gym and play ball at night when nobody was around." At that moment, that investigator is leading the group. He or she is trying to pick the lock, and if it turns out that there is a poisoned needle in the keyhole, then he or she is the one that gets stung by it. Now suppose that on the other side of the door is a mysterious leather bound book on a lectern. The investigator with the highest lore steps up and says "It appears to be a collection of Etruscan inscriptions. Based on the degree of vowel syncope, I'd date the writing at roughly 50 AD, although the book itself is clearly much newer." At this moment, the second investigator has stepped forward and is momentarily taking the lead: it is now this investigator that will try to read the book, and so it will be this investigator that is eaten first when the book turns out to be chock full of summoning spells (never, ever, break into a cult stronghold and start reading books aloud).

Cheers,
Chris

Thelric's analysis is correct. The "team leader" is essentially whoever "bad or good stuff happens to" if it's only a single person. The current team leader can delegate the responsibility for an activity to another person in the same area (thus, allowing investigators to cooperate), and it's only fair that, in turn, that investigator who takes the risks also gets to decide how the reward is spent.

Of course, in a truly cooperative group, that's not so important, but if you were doing, say, Arkham Investigations in tournament play, that specificity of the rules will probably come into play, since it needs to be unambiguous who is responsible for what decisions.

Personally, I think I am going to keep playing my houserule that the team leader can't be changed in the middle of a turn, but maybe increase the effectiveness of assisted checks. In my opinion, it defeats the purpose of having teams if you can swtich out the leader in the turn. Only my thoughts though