Shilsen is correct. the true strike spell only negates the "Miss chance" effect of being concealed. It does not negate anything else, it does not make fog go away, it does not make the target visible. If you do not have any idea where the target is, then you can't shoot at it. Unless you know where the target is, it's jst not possible. But after making a listen or spot check to know that somebody is invisible near you then the spell takes effect, the target still retains any other bonus' due to being invisible, you are still denied your dex if he attacks you, but the "Miss Chance" is negated if you manage to get a shot off.
1) Orc shaman in room is invisible.
2) Wizard with an extended true strike already cast enters room.
3) Wizard gets to make a spot check to see if he notices something out of place.
4) If he succeeds he can take a shot at the invisible orc, negating the miss chance of being invisible (the orc still retains any other effects of being invisible)
4a) If the wizard failed his spot check, he has no idea there is an invisible orc in the room and can not shoot at it.
True Strike does not confer the ability to see invisible things (that's a 2nd level spell) what it does do is "Negate the Miss Chance % of being concealed"
1) Orc shaman in room is invisible.
2) Wizard with an extended true strike already cast enters room.
3) Wizard gets to make a spot check to see if he notices something out of place.
4) If he succeeds he can take a shot at the invisible orc, negating the miss chance of being invisible (the orc still retains any other effects of being invisible)
4a) If the wizard failed his spot check, he has no idea there is an invisible orc in the room and can not shoot at it.
True Strike does not confer the ability to see invisible things (that's a 2nd level spell) what it does do is "Negate the Miss Chance % of being concealed"