penetrate her skin of efficient good humour

[jacdac]

He wondered if anything would penetrate her skin of efficient good humour. He couldn’t imagine her ever crying, for example. Had something in her past led to her forming this protective shell or was it a feature of her age and class?
Source: Thin Air by Ann Cleeves
Context: A dual criminal investigation is progressing. In this scene, a gathering of the English couples at their holiday house in Meoness in Unst was called by the investigating officers. They were gathered to check their reaction to the announcement of the murder of the local hotelier. Detective inspector Perez is gauging Caroline’s attitude and temper.


I am groping to understand the bolded text? What is considered efflicient good humour? Does ‘to penetrate one’s skin’ mean ‘to feel’?

Thank you

 

[The Newt]

She maintains a superficial aspect of good humour and efficiency, and he wonders if anything could penetrate that "skin." "Good humour" can't really be efficient or inefficient, but even though "efficient" is technically modifying "good humour" the author is really describing two distinct qualities of her deportment.

 

[kentix]

Good humour here means good attitude. It's not the same humor as when you laugh at a joke.

Her constant pleasant attitude might be efficient at preventing anyone from getting to know her more deeply. She's not unpleasant but she also doesn't let people inside her "bubble" it sounds like. She keeps them pleasantly at arm's length. She doesn't let people or things affect her too deeply. Or at least doesn't let it show.