How does the Detective archetype's True Confession ability work?

Question

The Detective archetype for the Bard has a True Confession ability. I do not understand one part of it:

Using this ability requires a successful Sense Motive check to see through a Bluff or notice mental compulsion.

How does that interact with the rest of the ability, namely:

After 3 continuous rounds of performance, the target must make a Will save (DC 10 + 1/2 the bard's level + the bard's Cha modifier). (...) On a failed save, a liar inadvertently reveals the lie and the truth behind it. A creature under a charm or compulsion reveals the nature of its enchantment and who placed it

As I read it, it means to use this against a Bluff or to detect mental compulsion (which sounds like all the cases you would use it for), you need to first succeed at a Sense Motive check against the usual DC and then, after 3 rounds, the victim gets a Will save and on a failure they reveal something.

Wouldn't the initial Sense Motive check reveal everything anyway if successful? If so, what's the purpose of this ability?

Answer 1

The basic Sense Motive skill gives you: "You know that's not true" or "You know the person is enchanted."

Sometimes that's enough. If it's a yes/no statement, knowing that yes is a lie gives you the answer. Or perhaps everyone nearby trusts your assessment of the truth over their own.

However, that doesn't cover everything. True confession gives you two additional benefits:

1. It tells you what the truth actually is (or, in the case of mental manipulation, who's behind it).

2. The target confesses, which makes it much easier to convince other people that he was lying.

Or, to put it another way:

I was beginning to get the feeling my partner wasn't acting in our best interests. There'd been a few too many things slipping by him lately. That, and he wasn't surprised when we got jumped.

Someone was definitely putting the screws to him. The only question was who?

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Benny the barrister was as crooked as they come. I know it, you know it, the mailman knows it, but so far I haven't been able to find any proof. I've used up all my good will with the sheriff... Either I get a confession out of this guy, or he walks.

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He said they went north. It was a lie. Anything to give his pals the time they needed to get away clean. I knew it was a lie, but that wasn't doing me a lot of good... "Not north" covers a lot of territory out here. Maybe if I work him a bit, I can weasel something useful out of him...

Answer 2

I read it exctly like you did. What is this extra check worth, then?

Sense motive just allows you to know someone is not telling you the truth.
Tricking him into telling the truth and even revealing who instructed him to lie should never be a result of the sense motive check, thus the utility of the True Confession ability.