In the County of Dorchester, there lived a daughter of the Earl of Derby, a widow lady, who had been the wife of John Arundel, commonly called the "Great Arundel." This chapter focuses on Arundell's work in conjunction with additional primary and secondary sources to trace her transition from an actively apostolic Catholic community, established by her mother and operating under conditions of secrecy in Post-Reformation England, to a cloistered convent in the heart of Catholic Brussels, the Benedictine Monastery of the Assumption of Our Lady, which she herself took part in establishing. Although the manuscript of Arundell's Life of Cornelius was long presumed to be held in the Jesuit Archives in Rome, a recent search has determined that it is now missing. The last person to mention consulting it was Richard Challoner, who reported that 'a copy' had been sent to him from St Omer, an outline of which he appended to his 1741 biography of Cornelius.