Catherine, a jovial, fun-loving, beautiful girl, had a past. She had grown up largely in the care of her grandmother, the Dowager Duchess of Norfolk - where supervision of noble wards was notoriously lax. The Dowager Duchess spent much of her time away, which meant that the young teenagers in her care were afforded more fun and freedoms than they otherwise might have been. She, along with other girls, spent a good amount of time with young men - even entertaining them in their bedchambers late into the evening. They would play music, dance, eat and drink, and generally have the same kind of fun that teenagers of today might have, when allowed to run a little wild.
Around 1536, Catherine began music lessons with a man named Henry Mannox, and historians have debated the exact nature of their relationship in the few years to come - but they definitely shared a sexual relationship of some kind. Both of them would, however, later deny that they ever engaged in actual intercourse. Much later, during Catherine's adultery inquisitions, she would confess, 'At the flattering and fair persuasions of Mannox, being but a young girl, I suffered him at sundry times to handle and touch the secret parts of my body, which neither became me with honesty to permit nor him to require.' These words would indicate that the sexual encounters were not entirely consensual - but given the nature of this confession, one might question whether or not Catherine played the victim to preserve some innocence, as she was being questioned about her sexual misconduct., and her royal marriage was, at this point, in jeopardy.
Her rise to queenship was swift, and when she married Henry in 1540, she likely felt that she had all the world at her fingertips. Henry absolutely doted on her - no doubt delighted that he, an overweight, old (for the time) man, had attracted such a lovely young lady to be his bride. He indulged and spoiled her, and his devotion to her was a stark contrast to his complete disinterest in his former wife. Guaranteed, he hoped for another son from Catherine, as his male heir, Edward (by his third wife, Jane Seymour), was three years old, and the future of the dynasty would only be strengthened by a spare.
But while Catherine was certainly subjected to performing her marital duty for the king, her affections were apparently stolen by the courtier, Thomas Culpeper - a young and handsome man, with whom she was probably having an affair by the spring of 1541. He referred to her as 'my little sweet fool' in love letters that were discovered during her downfall. One of Catherine's ladies-in-waiting, Jane Rochford (sister-in-law to the former Queen Anne Boleyn), arranged secret rendezvous between Catherine and Culpeper, and perhaps no one suspected a thing for several months... until autumn, when word reached the Archbishop of Canterbury regarding Catherine's previous sexual behavior under the Dowager Duchess's household.
During her adultery inquisition, Catherine claimed that her former lover, Francis Dereham, had raped her. She denied a precontract of marriage, but was nonetheless stripped of her 'Queen' title on 23 November. She was held at Syon Abbey while the king remained at Hampton Court, and within the next couple of weeks, both Francis Dereham and Thomas Culpeper were executed at Tyburn (Dereham was hanged, drawn, and quartered; while Culpeper was merely beheaded). As was custom, their heads were placed upon spikes on London Bridge, as warnings to London citizens that treason against King Henry VIII was no small thing.
Catherine was, no doubt, aware of these executions. She remained imprisoned throughout the winter and, on 7 February 1542, the Royal Assent by Commission Act 1541 was passed - making it treason and punishable by death for a queen consort not to disclose her sexual history to the king within the first twenty days of marriage, as well as to commit adultery against her royal husband. There was no need for a trial at this point - the evidence was stacked against her. Catherine Howard was sentenced to death.