Around Mar 1571 the Ridolphi Plot was a Catholic plan to assassinate Queen Elizabeth I of England and Ireland (age 37) and replace her with Mary Queen of Scots (age 28) would would marry Thomas Howard 4th Duke of Norfolk (age 34). Queen Elizabeth I of England and Ireland (age 37) and Thomas Howard 4th Duke of Norfolk (age 34) were cousins through their Great Grandmother Elizabeth Tilney Countess of Surrey.

On 29 Aug 1571 Norfolk's secretaries William Barker and Robert Higford entrusted to Thomas Browne, a Shrewsbury draper, what was purported to be a bag of silver coin for delivery to Laurence Bannister, one of Norfolk's officials in the north of England. Browne grew suspicious of the bag's weight, opened it, and discovered 600 pounds in gold from the French ambassador, destined for Scotland on Mary's behalf, and ciphered letters. Because he knew Norfolk was under suspicion, Browne reported his find to William Cecil 1st Baron Burghley (age 50), the Secretary of State. Higford and Barker were interrogated, the letters were partly deciphered, and a search for the cipher key at Howard House uncovered a ciphered letter from Mary Stuart hidden under a doormat.

On 07 Sep 1571 Thomas Howard 4th Duke of Norfolk (age 35) was imprisoned at Tower of London [Map] for his involvement in the Ridolphi Plot.

Around Sep 1571 William Brooke 10th Baron Cobham (age 43) was implicated in the Ridolphi Plot and imprisoned at home for months.