Neil Aldridge is a Doctor of Physics.
Kestrel is an elite EU special forces team.
Dealing with the second introduction first, we learn about Kestrel some time after the first adventure begins that. We learn about it from a Captain Jessica Greenwood who is kind enough to explain about the organization soon her introduction. First is that Kestrel is a covert group attached to EUFOR, though not part of it.
This begs the question as to what EUFOR is. We are instructed that "EUFOR was the blanket term for the European Union's rapid reaction forces, one of several military forces operated by the EU as part of its Common Security and Defence Policy." We also are informed that it "had a gendarmerie, a maritime force, and even a standing army called Eurocorps, with dedicated battlegroups and specialist teams supplied by various member nations."
Back on the matter of Kestrel, Greenwood explains, "We're an elite surveillance, infiltration and combat force operating under the direct authority of the European Security Council. Our official title is the European Special Tactical Force, Group One, but anyone who knows that name will deny our existence."
All this information is being explained to the man introduced above first, Neil Aldridge. Aldridge is not part of Kestrel, as evidenced by the fact that the explanations mentioned above were directed by Greenwood to him, but we will watch as he plays as big a role in the adventures as Kestrel itself, enough to be given, IMHO, the starring role.
Neil Aldridge is a lecturer in the School of Physics and Astronomy at the University of Edinburgh. He is "37 years old. His PhD in theoretical subatomic particle physics entitled him to be addressed as Doctor, but he shunned that appellation. It was too damned pompous by half, and made him feel ridiculous".
He will be brought into the danger and excitement that seems to be a constant condition for the people of Kestrel because of his uncle who was also a physicist and who ran afoul of a very nasty and ambitious man and who appealed to Aldridge for help. Luckily for Aldridge, Kestrel was already keeping watch on all the players and stepped in when needed.
Which explains how and why a Physics lecturer became intimately involved with a force like Kestrel.