In May 1654 Vowell, Summerset Fox and John Gerard, from Islington, were arrested for their part in Gerard's conspiracy, a plot to overwhelm the bodyguard of the Lord ProtectorOliver Cromwell with 30 mounted men as he travelled to Hampton Court and assassinate him. The allegation against Vowell was that he was to help seize the horses while they grazed in Islington fields. The Government received intelligence of the plot and arrests were made.[1][2]