Working on the theory that the Princes in the Tower disappeared but did not necessarily perish, there is some historical evidence that at least one of them survived.
Let’s start with the ‘feigned boys’ that caused Henry VII so much trouble. In order for any of them to be able to threaten his position, it must be assumed that people had reasons for thinking the princes were still alive. He was unable to display any bodies, and their mother, Elizabeth Woodville, never, at any time, accused anyone of murdering them. Additionally, the man who would logically have been the Yorkist heir, John, Earl of Lincoln never put forth his own claim, which might indicate that he knew someone with a better one was still around.
First up, in 1486, was a child the Yorkists primed to portray the princes’ cousin Edward, Earl of Warwick, but since Henry happened to have the real Warwick safely in custody, parading him before the populace and discrediting the pretender wasn’t a problem. (It has always struck me as strange that anyone would have even tried to have a kid impersonate the little Earl of Warwick, as it must have been well-known that Henry could produce the genuine article at any time. The original plan had been for the boy, Lambert Simnel, to be presented as one of the missing princes, which would have made more sense as Henry couldn’t produce them.)
Later, however, a ‘prince’ came along who couldn’t be so easily dismissed. In 1491, a young man turned up in Ireland and proclaimed himself Richard, Duke of York, the younger of the Tower princes. His physical appearance, royal manner, and detailed memories seemed so credible that by 1492, he had the backing of several royal personages, including Charles VIII of France, Margaret, Dowager Duchess of Burgundy (aunt of the two missing princes), the Holy Roman Emperor Maximilian, and King James IV of Scotland, who must have been really convinced, since he allowed him to marry one of his own kinswomen, an unlikely move if he doubted his authenticity. (High-born ladies weren’t bestowed on just anyone.) The armies raised on his behalf failed to defeat Henry’s forces however, and in September of 1497 he was captured and made to confess that he had been tutored in his royal role and was really Perkin Warbeck, the son of a Flemish merchant. But torture, or the threat of it, can result in false confessions, so even after he and the unfortunate Earl of Warwick were executed in 1499, there were people who believed he really was the Duke of York. Many still do today.
Besides ‘pretenders’, there was also a bricklayer in Eastwell, Kent who might have been a Tower prince. This bricklayer could read – in Latin – an accomplishment not generally associated with one of his station, and shortly before his death in 1550, he hinted at a secret royal connection. He was buried under the name Richard Plantagenet, but his supposed age of eighty-one puts him closer to the age Edward V would have been in 1550.
Either of the above could have been one of the Princes in the Tower if the princes were secretly removed from there. As could people who never attracted attention of any kind and never became the subject of speculation. Unfortunately, it is also possible that they met their end at the hands of assassins and their remains are now in that urn in Westminster or are secretly buried in a place that has yet to be discovered.
Time Travelling With Kids 
Certainly one of the greatest mysteries of history. Your speculative book on the Princes provides a wild idea, but who knows? Time travel is certainly an intriguing and long-lived theme in science fiction.