After this, Carstares visited Ireland, joined nonconformist circles in London, and then in 1681 became pastor to a congregation at Theobalds, near Cheshunt in Hertfordshire. The aftermath of the Exclusion Crisis saw him directly involved in conspiracy with the Whig faction. Archibald Campbell, 9th Earl of Argyll in the Netherlands was in touch with Anthony Ashley Cooper, 1st Earl of Shaftesbury. Carstares provided liaison, while his brother-in-law William Dunlop was able to use his colonial project in the Province of Carolina as cover for Shaftesbury's preparations for rebellion.