But there is one condition

[kachibibb]

Say, there is a witch saying that she can make an old woman young again on the condition that the old woman helps the witch find a treasure.

So, there is a condition.

Is the following idiomatic?

The witch says, "I can help you (the old woman) young again. But there is one condition. The condition is that you help me find the treasure."

 

[tedmc]

I can help you become young again on one condition.

or

I can make you young again on one condition.

 

[kachibibb]

So saying "condition" explicitly is really idiomatic?

 

[Rover_KE]

It's too early to draw any conclusion on the basis of a single response.

 

[jutfrank]

Yes, But there is one condition is correct.