The long and short of it is this: [but one bit of pertinent out-of-club detail is missing]

1) Mike Brown and the club were in contract negotiations. Brown had rejected the first offer from the club (from early 2020), and was chasing them to talk about it for quite some time.
A) Imposition of reduced salary cap
2) In December, Quins changed their mind about offering Brown any kind of contract, decided he was surplus to requirements at the club, and told Mike Brown this.
3) Brown was understandably surprised and hurt by this, and ends up talking to Dean Richards, and they agree Brown will join Falcons on a contract that Brown is happy with.
4) Paul Gustard gets binned off.
5) Quins belatedly realise they've made a mistake and come back with some reduced offers, which Brown rejects because he's already agreed to join Falcons.
B) Quins improve. Brown's personal form is excellent.

[Bold Italic text is my addition]

I think that salary cap announcement needs inserting (reduced cap must have had some effect on salaries, especially older members, how ever good/great they may have been/may still be) and the time lines need minor amending.