"I am writing to apologize for the unfortunate incident that occurred shortly after our family concluded grace at our Thanksgiving celebration" Note that the thirteenth word is 'after', not 'alter'. 'Alter' makes no sense here. The phrase "shortly after our family concluded grace at our Thanksgiving celebration" specifies WHEN the incident happened : Within that, we have the simple SVO phrase "our family concluded grace": Subject = our family Verb = concluded ( meaning finished) Object = grace ( meaning the prayer usually recited before a meal) In other words, something awkward happened during the Thanksgiving celebration, just after the family had finished saying their prayer.

"Grace" is a prayer said by Christians before a meal to thank God for the food: The children always say grace at dinnertime. https://dictionary.cambridge.org/dictionary/english/grace