Whether it's Avalon, Star Antimony, or the Iris Flower, when they actually locate spies, they often don't immediately apprehend them. Instead, they follow the trail to hunt for more evidence or even take control of the information being sent back by the spy.
When their own spies are captured overseas, they would immediately arrest some spies under surveillance and engage in a hostage exchange with the other side.
Spies are obligated to keep secrets during interrogation, and the agencies behind the spies are also obliged to ransom their captured spies back.
Usually, the exchange is one for one, but if an important spy is caught, they can demand a two-for-one or even a three-for-one exchange.
However, Sherlock leaving Watson behind wasn't because of his personal friendship with Dr. Watson.
It was because of another very important matter which the Queen also knew about.
