Before the line "And they have conspired together" (II,5,l.23), Launcelot (unaware of his malapropism, by the way), says to Shylock, "My young master doth expect your reproach" (ll.20,21). This is a reference to Bassanio, who has recently replaced Shylock as Launcelot's boss. Considering this -- as well as the dramatis personae of scene 6 -- the "they" of line 23 must refer to Bassanio and his coterie, (a group consisting principally of Antonio, Lorenzo and Gratiano). The "conspiracy" Launcelot mentions refers to Bassanio's plan to participate, along with his fellow Christians, in a "masque," a large-scale and public display of revelry, (probably what is considered the "Carnivale" in modern-day Venice). The party never happens, however, as Bassanio (along with Gratiano) decides to sail that night for Belmont.