WHAT DANGERS DEEP is written as a first-person memoir of Sir Philip Sidney, in which he recalls his time spent in Krakow, Poland in 1574 at the end of his European tour. Sidney was born in into an important British family during momentous times, two of his godparents were Philip I of Spain (for whom he was named) and "Bloody" Mary Tudor, and he was the nephew of Robert Dudley, love of Elizabeth I's life. Sidney is well known in academic circles for his writings and poetry, but like most people, I had never heard of him before reading this novel. I looked him up on the Internet and was surprised by the amount of material about his writings and his life.

At this time Poland is without a king (Henri of France deserted the throne) and the powerful lords are vying with one another for control. The Poland Philip encounters is a hotbed of social conflicts: Catholics and Protestants, new medical and scientific colleges and occult studies that are anathema in England or France, and always the threat of invasion by the nearby Turks.

Young Philip is ostensibly in Krakow for his other godfather Antony's wedding, but he is secretly carrying a message from Queen Elizabeth to the exiled Catholic priest and professor Caspar Laurence. Sidney is attacked several times by someone presumably looking for the message.

While waiting for the priest to return to the college so that he may deliver his message, Philip spends time with Antony's new sisters-in-law, Yolanta and Maria, who are close to his own age. He grows to know and care for the girls deeply, orphans who are being raised by their uncle Pan Jan Zamoyski, the most powerful lord in Krakow.

When the sisters take Philip to see the local sights, disaster strikes. They visit a spring called the Ancient Mass, which has been considered a holy site for millennia. When Philip bends to drink the water, something bizarre happens to him, and when he comes back to his senses a couple of minutes later, the girls have both disappeared.

A vast search is instigated, but there is no sign of the girls, and no clues as to what happened to them. The tensions already simmering in Krakow boil over - directed at the prime suspect - Philip. He finally manages to make it back to the spring some days later to conduct his own investigation and finds an insensible Maria lying next to the spring. There is still no sign of her sister Yolanta.

Philip delays his return to England despite Queen Elizabeth's and his family's urgings, determined to get to the bottom of the mystery of Yolanta's disappearance. However, Maria never remembers anything more than a sensation of falling into light and Yolanta is never seen again. A dejected Sidney finally returns home to his queen's service. ( )