In 1568, Carew embarked on his greatest adventure, when he laid claim to lands in the south of Ireland. He had sent ancient documents for examination by John Hooker, who became convinced – after travelling to Ireland – that the documents established Carew's hereditary entitlement to extensive properties in that country. Henry II of England (the first Lord of Ireland, a title assumed in 1172 at the beginning of the Cambro-Norman conquest) had granted half the lordship of Cork to Robert FitzStephen, and Hooker believed that Fitz-Stephen's daughter had married a Carew ancestor. Carew's claim existed by letter of the law contained in antique parchment under crown seal.