Tom Walsingham is an agent with British Intelligence.
Since the year we first encounter him is 1581, there is no established department by that or any other name in Her Majesty's government tasked with intelligence gathering both internally and externally. There most decidedly exists the need for one since the Queen's enemies are many and several of them are quite powerful. The nations of the Netherlands and France and Spain would all love to take from England anything they can and inside the island nation are scores of angry Catholic citizens who would prefer a Papist on the throne.
Helping to keep the status quo is the monarch's personal Secretary, Sir Francis Walsingham, who in addition to his many duties in his public job has taken on the unspoken role of Royal Spymaster. Over a good number of years he has extended his figurative tentacles through the Kingdom and well into Europe and his clandestine eyes and ears keep him very well informed.
One of his many agents is also one of Sir Francis' favorites, a fairly distant much younger cousin named Tom Walsingham. For the past two years, since the young man was just turning 17, he has been in close training and has shown considerable potential. So much so that on our first encounter, he has been given a solo mission of some importance.
Importance is a noun not previously used very often with young Walsingham though not through any failings on his personal part. He was a third son and as such was out of the running for any inheritance, if there was any to begin with. His prospects were hardly any better, at least until Sir Francis took a liking to him and brought him in to begin training him in clandestine services. What neither Sir Francis nor Tom would have thought of was the fact that the teenage daughter of Sir Francis would have taken her own form of interest in Tom and vice versa.
Young Tom will prove himself a very effective operative though being new to the trade he will make mistakes and occasionally put his trust in those not deserving of it. He will be smart and clever enough to overcome his errors.