Cavehill

They start as a reform society.

They then have a meeting famously on Cave Hill where Wolfe Tone-

That's right, Thomas Russell

... and Henry Joy McCracken-

In the aftermath of the rebellion's defeat, Belfast was placed under military curfew and Henry McCracken vanished into hiding with a bounty on his head.

Knowing that he and his friends were likely hiding yet hungry and scared, Marianne stole out into the curfewed streets and took herself at great risk up to the hills surrounding Belfast until she found her brother on Cave Hill.

Marianne brought him clothes and helped keep him hidden until they could get him to a boat that would take Henry to safety in America.

On her 28th birthday, Mary Anne received the news that their plan to get Henry out of the country had failed.