Agnes Fisher married Oliver St John, a son of Sir John St John and Margaret Waldegrave. Oliver St John became 1st Baron St John of Bletso, and was also known as Lord St John of Bletso.

By his father, Oliver St John was a descendant of Roger de Beauchamp, Baron Beauchamp.

Oliver St John was raised to the peerage as Baron St John of Bletso, in the county of Bedfordshire, on January 13, 1559.

Oliver St John was born circa 1522 at Bletsoe, Bedfordshire. He died on April 21, 1582.

Agnes Fisher was his first wife. Oliver St John next was married to Elizabeth Chamber.

Children:
John St John, 2nd Baron St John of Bletso
Oliver St John, 3rd Baron St John of Bletso
Thomas St John
Francis St John
Martha St John
Judith St John
Margaret St John
Anne St John
Margery St John
Agnes St John

Oliver St John of Bletsoe, 1st Baron St John of Bletso (c. 1522 – April 21, 1582) was an English peer. Son of Sir John St John (born 1498), of Bletsoe and Spelsbury and his first wife Margaret, daughter of Sir William Waldegrave. 

Oliver St John was a direct descendant of Sir Oliver St John of Bletsoe, Spelsbury and Lydiard Tregoze (d. 1437) and Margaret Beauchamp of Bletso — his third great-grandparents on the side of his father John St John.

Margaret Beauchamp was a second great-granddaughter of Roger de Beauchamp, summoned to Parliament as "Baron Beauchamp of Bletso" in 1363-1379.

Roger de Beauchamp's title Baron Beauchamp had not been assumed since his lifetime, though (Agnes Fisher St John's husband) Oliver St John was considered to be in the line of heir to this title.

On January 13, 1559, Oliver St John became, in his own right, "Baron St John of Bletso in the county of Bedfordshire".

He served in the household of Prince Edward and on his master's accession as Edward VI in 1547, he entered the royal household.[1] He was elected as knight of the shire (MP) for Bedfordshire in 1547.[1] He served as High Sheriff of Bedfordshire and Buckinghamshire in 1551 and from 1560 to 1569 was Lord Lieutenant of Bedfordshire.[3]

Offices held by Oliver St John during his career included:

• Gentleman waiter extraordinary, household of Prince Edward (by 1547)

• Gentleman waiter extraordinary, royal household (1547)

• Commissioner, relief, Bedfordshire (1550)

• Commissioner, musters (1560)

• Commissioner, ecclesiastical causes, dioceses of Lincoln and Peterborough (1571, 1575)

• High Sheriff of Bedfordshire and Buckinghamshire (1551–1552)

• Justice of the Peace:
Bedfordshire 1554–1558, q. 1558/59 1582
Cambridgeshire, Huntingdonshire 1562–1582

• Custos rotulorum, Bedfordshire 1558-1559

• Lord Lieutenant, Bedfordshire 1569

Lord St John of Bletso married twice. He married firstly, before 8 February 1542, Agnes, the daughter of Sir John Fisher, and by her had four sons and six daughters:
• John St John, 2nd Baron St John of Bletso
• Oliver St John, 3rd Baron St John of Bletso
• Thomas St John, of Thurley, Bed. (inherited when St. John of Thurley became extinct; Thomas St. John of Thurley was named as brother to Judith St. John Pelham); married Anne Bourne, widow of Thomas Chicheley and daughter of Sir John Bourne. Thomas St. John was buried 27 Dec 1621. Had at least two children: Oliver St. John and Anne St. John. He also had several step-children.
• Francis St John
• Martha St John married firstly, John Cheney and secondly, James Colbrond
• Judith St John married Sir John Pelham
• Margaret St John married Nicholas Luke
• Anne St John married firstly, Robert Corbet and secondly, Sir Robert Lytton
• Margery St John
• Agnes St John

OLIVER ST JOHN, Lord St John of Bletso, next married, before 28 August 1572, Elizabeth, the daughter of Geoffrey Chamber, and widow of Sir Walter Stonor (died 1551), Reginald Conyers (died 1560) and Edward Griffin (died 1569).

Oliver St John died on 21 April 1582 and was succeeded in the barony by his eldest son John.
https://en.m.wikipedia.org/wiki/Oliver_St_John,_1st_Baron_St_John_of_Bletso

Wikipedia is source for most information in this biography. Further reading and research using primary sources is suggested.