words - why is でのこと used?

I have two questions regarding the opening lines of a short story called 真夜中の王女(midnight princess)

ある王国でのこと。
うつくしい王女が十五歳でなくなって、そのなきがらをおさめたひつぎが、教会にはこびこまれた。

1. Is the use of でのこと just to give the impression that something is happening or taking place.



2. Is the verb associated with object marker をおさめた 収める？And if so is なきがらをおさめたひつぎが a polite set phrase that means the burial casket. or is the literal meaning they want because it is a horror story therefore it would be something like corpse interned coffin.

so my interpretation is, In a kingdom a 15 year old beautiful princess passed away and her corpse interned casket was carried to the church.

Answer

For your first question, 王国のこと would just refer to "something about a certain kingdom". Adding で to get "王国でのこと" means "something that happened in a certain kingdom".

To give a similar example "バスでの旅行" means "a trip via a bus". Removing the で here would mean just "a trip of a bus".

So yes, your interpretation of this point is generally correct.

Since this looks like a fairy tale, if you were doing a proper translation you might use a more appropriate English phrase, like "Once upon a time in a kingdom".

For your second question, I think Choco's comment confirms the usage of the verb おさめる in question here.

I would translate this part more as "the coffin carrying the princess's body..."