Sheriff Tate had received word that Tom Robinson was going to be transferred to the Maycomb County jail, and he had come to Atticus's house to give him the news. Other concerned citizens had followed him to show their support, and they congregated in Atticus's front yard.
In Maycomb, grown men stood outside in the front yard for only two reasons: death and politics. I wondered who had died.
Tate worried that there might be some sort of trouble, but Atticus tried to make light of the situation.
"Don't be foolish, Heck," Atticus said. "This is Maycomb...
"I don't think anybody in Maycomb'll begrudge me a client, with times this hard."
Link Deas, who was also present, agreed with Atticus, but he added that
"... it's that Old Sarum bunch I'm worried about...."
The Sheriff's and Mr. Deas's worries were not unfounded, and the next night the sheriff was called away on a "snipe hunt," leaving Atticus to defend Tom alone at the jail when another group of men arrived--men from Old Sarum.
The peace at Atticus' house is interrupted one night when Sheriff Tate and several other men from Maycomb arrive at the door to speak with Atticus about the possibility of trouble in town. The men are prompted to visit Atticus out of concern for Atticus' well-being as well as out of concern for the peace of Maycomb.
The catalyst of this concern is the transfer of Tom Robinson, Atticus' black client who has been accused of rape, to the Maycomb jail to await trial. Although the stay at the Maycomb jail will be a short one, Sheriff Tate and the men are convinced that trouble may erupt when some people hear about the transfer. Atticus is certain that the sheriff can keep Tom safe, but Sheriff Tate communicates that it is a certain family, The Cunninghams, who he feels may attempt to lead a lynch mob.
To Jem and Scout watching from the living room windows, the men in the crowd who at first appear concerned begin to appear threatening as Atticus disagrees with them. Jem eventually interjects that Atticus has a phone call, at which point the crowd disperses.
Tate and the other men, including Link Deas and Dr Reynolds, come to visit Atticus to tell him that trouble might be brewing. Tom Robinson is being transferred to Maycomb County Jail just before the trial and there is the possibility that some men from the town will try to lynch him. Atticus doesn't appear unduly concerned, but his visitors inform him that the Cunninghams from Old Sarum will likely attempt violence.
The attitude of the men towards Atticus seems to be one of concern; they want to warn him, and are offering support. However it all begins to look distinctly 'ominous' to the children, who are watching from the window. From their perspective it seems as though the men are ganging up on Atticus:
There was a murmur among the group of men, made more ominous when Atticus moved back to the bottom front step and the men drew nearer to him. (chapter 15)
Jem attempts to avert any trouble by shouting out that the phone is ringing. Atticus merely tells him to answer it, and the men laugh and begin to scatter. At this point the children realize that these are all familiar faces and that Atticus was never in any danger from them.
However, their warnings are well-founded and the Cunninghams from Old Sarum do indeed lead a lynching party to the jail at night. Atticus is there alone to defend Tom Robinson, until his children, drawn by curiosity, also come along. The situation is about to turn ugly but Scout unwittingly intervenes and defuses the hostility. This time the men are not familiar to the children - except for the father of Walter Cunningham, Scout's classmate. Unaware of what is really going on, she tries to make polite conversation and in her innocence completely turns him and the others away from their grim purpose.