Start of briefing is not as in agenda: answer party with opening issue at table (3-7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

1st letter of ( Start of ) “ briefing ” + II(2 x the letter “i”/is) replacing ( … not … in ) “aa”(2 x letter “a”/as) in “agenda” + ANS(abbrev. for “answer”). Answer: In Jonathan Swift’s Gulliver’s Travels, the group/party of people in Lilliput who believed that boiled eggs should be broken at the big end, rather than the small, as commanded by the Emperor of Lilliput. This could thus be described as an opening issue at the dining table.