Despite the fact that she's been dead for over four hundred years, Mary, Queen of Scots remains a controversial and divisive figure amongst historians.
The only surviving child of King James V of Scotland and Mary of Guise, the younger Mary started off her reign much the same way her father had. James's father, King James IV, died in 1542 at the disastrous (for the Scots, at least) Battle of Flodden Field, making James V the king in 1513 at the age of only seventeen months. This put the kingdom in the hands of regents throughout the early years of the reign, which is seldom a recipe for stability. After much jockeying about by regents and councillors eager to wield control, James V finally was able to throw off the shackles of the regency in 1528 following the Battle of Linlithgow Bridge.
His adult reign was turbulent. James himself has been characterized as paranoid (unsurprising, really, considering that he'd been a virtual prisoner to his regents as a child), more interested in reading and playing the lute than in administering a kingdom. He did have a great concern for the common folk, however, and actually spent time wandering amongst them in disguise, gaining him the nickname of "the Gudeman of Ballengeich" ("gudeman" is Scots dialect for "smallholder;" Ballengeich is one of his favorite haunts, near Stirling Castle). Interestingly, there's a sweet Scottish country dance tune called "The Geud Man of Ballengigh" which I've known for years -- knew the tune, in fact, long before I ever knew the story behind it.
James V died in 1542, at the age of only thirty, probably of cholera -- only six days after the birth of his daughter Mary. Mary was crowned, just like her father had been, as an infant. This once again left Scotland in the hands of regents, headed by her mother, the smart, powerful Mary of Guise, who (unlike the regents James had endured) was determined to hang onto the throne on the behalf of her daughter. Mary was sent off to France to be raised and educated, something that was to work against her later, as culturally she was seen as far more French than she was Scottish. This was amplified in 1558 when she was married to King Francis II of France, but that marriage was ended by Francis's death in 1560 at age sixteen (whether of an infection or because he was poisoned is uncertain). The marriage produced no children; some believe it was never consummated.
Then Mary of Guise died in 1560, at which point the younger Mary -- now widowed and old enough to rule Scotland in her own right -- returned to her home country, which she'd barely seen in her eighteen years. But as with her father, she found that the powerful men who had run the country in her absence weren't eager to give up control. Mary then showed signs of the recklessness that was to characterize the rest of her life. She first married the wildly unpopular Henry Stuart, Lord Darnley, who was actually Mary's half first cousin (Mary's paternal grandmother, Margaret Tudor, daughter of English King Henry VII, had married twice -- first to King James IV of Scotland, and second to Archibald Douglas, Sixth Earl of Angus; those two marriages produced Mary's father, and Darnley's mother, respectively.) The marriage, by all accounts, was miserable. Despite being handsome and superficially charming, Darnley turned out to be a vain, arrogant, violent drunkard. In fact, when Darnley was murdered by a group of noblemen led by James Hepburn, Fourth Earl of Boswell in 1567 -- only a year after the birth of Mary's and Darnley's only son, James (eventually King James VI of Scotland and James I of England), Mary turned around and married Hepburn a month later.
This outrage was the final straw. Darnley had been unpopular, but the queen marrying his murderer was just too much. There was a massive uprising, and Mary was forced to abdicate in favor of her infant son (making for three infant successions to the throne of Scotland in a row). She fled to England, asking for asylum from her cousin, Queen Elizabeth I (Elizabeth's father, King Henry VIII, was Mary's paternal grandmother's brother). Elizabeth reluctantly agreed, but recognizing the fact that Mary was a direct descendant of King Henry VII and thus in line for the throne, she had her put under rather genteel house arrest.
Her caution is understandable. Elizabeth's own path to the throne had been fraught, and for a while it looked likely that she herself was going to spend her life in close confinement (if not worse). But when her two half-siblings, King Edward VI and Queen Mary I, both died without heirs, she succeeded to the throne for what would be one of the longest and most successful reigns of any monarch of England.
Mary, though, wasn't content to relax into what was honestly a fairly comfortable situation and give up her aspirations to rule. In fact, she was of the opinion that Elizabeth's own reign wasn't valid; the marriage between Henry VIII and Elizabeth's mother, the unfortunate Anne Boleyn, had been annulled shortly before Anne lost her head on Tower Hill, making Elizabeth effectively an illegitimate child. So Mary, ever the schemer, started writing letters to perceived supporters, trying to garner support to overthrow Elizabeth and put Mary on the throne of a combined England and Scotland.
It's those letters that are why the topic comes up; while some were written (unfortunately for Mary, as it turned out) in plain English, French, or Italian, some were written in code -- and until now, they'd been undeciphered. But a team made up of George Lasry of Israel, Norbert Biermann of Germany, and Satoshi Tomokiyo of Japan have finally cracked Mary's cipher and allowed us to discover more about her plotting to do in her cousin -- a plot that, as I'm sure you know, ultimately failed spectacularly.