In that type of situation, if a new member joins the group who is not familiar with the topic and with no one from the group, then in fact the group itself is frozen at the Norming point stage. The process is frozen at the Norming point, and not rolled back to the previous ones, because the initial composition of the group: they know each other well, they know what to do and how to do to complete the task. The group only needs to bring the new member up to date, and the new member to meet his new colleagues. Further, the process of completing the task, in most cases, depends on the new participant, how he will join the team and how he will work in it. However, one should not exclude the possibility that the initial team should be obliged to tell well what they have already achieved and honestly redistribute responsibilities. Failure to do this kind of thing on the part of the original composition of the group and the new member of the group threatens to slow down the process of the completing the task.
New members of the group who join the group at the Norming stage, they need to show that they are ready to work in a team on this task. They need to carefully study what the group has already done, what it plans to do, and thus slowly become part of the team. There was a case when a new member was added to the group in which I was a member. We met, said who is looking for and writes in our general report, showed and told what we have already done and what plans to do. The new participant listened attentively to us, got acquainted with the material already written, helped edit what was there and looked for new information for the general report.