The ingénue police are at my door.

Is this Melissa Errico? The actress? Do you understand that Sharon in “Finian’s Rainbow” should be around 27 years old? Would you please come with us?

Then I wake up.

Sleeping actors are known to forget their lines, or what play they are in, or where their pants have gone. When I was offered the chance to perk up my curly curls and scrub up my Irish brogue to portray the fairylike Sharon McLonergan in a coming Off Broadway revival of the musical “Finian’s Rainbow,” this version of the actor’s dream crept into my subconscious and made plain thoughts I was already thinking: At age 46, when does an ingénue hang up her ponytail? When is it time to stop dancing with leprechauns?

What is an ingénue in a musical? Sharon, a role I’ve already played twice, is typical of the kind. She’s the young lady who might end up with a nice-looking tenor. She has a high lyric soprano, big eyes, long hair and a figure that is conventionally attractive but not wildly attractive — neither voluptuous nor what you would call sexy. An ingénue is candid and innocent. A little waistline is good, and she certainly isn’t a mother yet. Leggy is for the funny or dangerous characters.