Plot devices in role playing games include things like: the party is sent on a quest of some sort, the party is given the opportunity to do some exploring, the party is going to get paid for doing something, or the party notices strange happenings and goes to investigate. Also, one of the party members gets captured and must be rescued, one of the party members is being pursued by someone or something, or one of the party members has a dark secret which might have all sorts of nasty consequences if it gets out. The weaving together of plot devices makes a plot (usually).