A Courier is one of the role archtypes that a participant in a plot can have. The Courier is a simple middle-man who receives one or more items from one participant (usually a Minor Agent), and passes them on to another participant. Couriers do not participate in the crime itself, and are only meant to add a link in the chain of the Master Plan.
A Courier is any agent whose only role is to receive an item from one participant and then pass it on to another. They never participate in any crime.
The source of the item to be relayed is usually a Minor Agent, who has commited a minor crime in order to get that item. Other sources include Paymasters, who acquire a cash Payoff through a bank transaction.
The target of the item is usually the Major Agent of the plot. However, if the item to be carried was created during the Primary Crime, the delivery target will usually be the Mastermind or some other high-operative waiting to get his hands on the goods.
Appearance in PlotsEdit
Couriers do not appear in every plot. Where they do appear, it seems that their only purpose is to make the plot more complex, adding another link in the chain.
They will usually remain anonymous until such time that an item is passed into their possession. This can be helpful, because item transfers are often accompanied by bulletins from the CIA Airport Surveillance letting you know that enemy agents are traveling around. This occurs because the source agent has to actually meet the Courier in order to deliver an item.
Once the Courier has successfully delivered all the items he's supposed to deliver, he will attempt to go into hiding at the next opportunity. This can only be prevented if the item is confiscated, and only if the source of that particular item hasn't been arrested or gone into hiding yet (and thus, can re-acquire the item and initiate the courier transfer a second time). This can be repeated indefinitely, as long as the source and the Courier are both at large. If the target of the delivery has been arrested or gone into hiding, the Courier himself will disappear together with the item as soon as the opportunity arises.
Rank and ScoringEdit
Couriers are usually low-ranked operatives, and capturing one does not offer many points. However, the item they are delivering is, as always, worth a considerable number of points (much more than the Courier himself) the first time you confiscate it.
Couriers are themselves not a very lucrative target. They simply offer another target that can be taken down. This can complicate you mission a little, by adding another agent to track down and arrest.
However, there are several benefits to the existence of a Courier in the Master Plan. For one, if you allow the Courier to successfully deliver an item at least once, you are very likely to be able to deduce both the origin and destination of that item, netting you the locations of two plot participants. This is particularly true because item delivery happens in person, I.E. the source agent has to meet the courier to deliver the item, and the Courier needs to meet the target agent to complete the delivery. The CIA Airport Surveillance team will put out a bulletin each time this occurs, since they will observe these agents moving from their original locations.
On the downside, such bulletins will usually inform you of the location of the source agent, not the Courier, but that may be enough to help you piece together where the Courier, and hence the item, currently is.
Another benefit is that the plot chain becomes longer, allowing you more time to gather important information while the item makes its way up the chain. If you act quickly enough, you can capture the item in any of three locations (the source, the Courier, or the destination) to delay the progress of the plot by a few days. Of course, if you take too long, it's likely that the Source agent will go into hiding by the time the item is delivered to its destination, so don't expect this to be a cake-walk.
One final thing to note is that sometimes Couriers act as middle-men between the Major Agent and the Mastermind. By tracking such a delivery, you can easily locate the Mastermind and may have enough time to catch him before he goes into hiding with the item. However, note that for this to occur the Primary Crime of the plot will probably need to have been perpetrated, costing you a lot of points. It's a good way to save a "gone-horribly-wrong" mission and get off with "not very successful" instead.