| agent(noun, plant, operative, informer) |
| secret agent(noun, expression, plant, agent) |
| double agent(noun, expression, plant, agent) |
| detective(noun, plant, watch, agent) |
| emissary(noun, plant, watch, agent) |
| informer(noun, plant, agent, operative) |
| intelligencer(noun, plant, agent, operative) |
| lookout(noun, plant, watch, agent) |
| mole(noun, plant, watch, agent) |
| operative(noun, plant, agent, mole) |
| patrol(noun, plant, watch, agent) |
| picket(noun, plant, watch, agent) |
| plant(noun, agent, operative, informer) |
| scout(noun, plant, watch, agent) |
| sleeper(noun, plant, agent, operative) |
| sleuth(noun, plant, watch, agent) |
| snoop(noun, plant, agent, operative) |
| spotter(noun, plant, watch, agent) |
| advance(watch, lookout) |
| adventurer(watch, lookout) |