"Old Dogs" gives groups fun thematic options of dealing with agents that might have gotten too powerful to go on missions with their former peers.
The supplement gives you examples of how to determine when a character might be considered an "old dog" and even more options of what to do with them once they are. The options include a career change to a instructor of the next generation of agents or maybe sending the veterans into outerspace to fight to the death against aliens.
It offers a few mechanical tools in the form of high level enemies and a couple of different options to alter advancement methods, but the core of this zine is creative thinking. This zine jumpstarts the conversation about high level play and brings a lot of fun options to tables dealing with it for the first time. Definitely recommend reading.