Final answer:
Lady Macbeth is the character who joins the assembled group in Macbeth's place during a scene in Shakespeare's play 'Macbeth'.
Step-by-step explanation:
The character who joins the assembled group, sitting in Macbeth's place, is none other than Lady Macbeth. In the play 'Macbeth' by William Shakespeare, Lady Macbeth is a pivotal character who is deeply involved in the plot and machinations surrounding her husband, Macbeth. The dynamics of the duo's relationship and Lady Macbeth's own ambitious drive play a central role in the unfolding of events, especially in their host's hospitality towards King Duncan, and the subsequent decision to murder him to claim the throne.