The three remaining guests eat breakfast in the kitchen. The storm has passed, and Lombard suggests that they try signaling the mainland from the top of the hill. He adds that they might also try making a bonfire in the evening. Claythorne states that someone is bound to see a signal and rescue them before nightfall, but Lombard notes that the sea is still far too rough for a boat to come to the island. Claythorne can't bear the thought of spending another night on the island. Blore raises the issue of Armstrong. When Lombard asserts that Armstrong must be dead, Claythorne questions why they haven't found his body. Lombard and Blore argue over what might have happened to Armstrong, with each subtly accusing the other of having murdered Armstrong. Blore turns his comments to the reappearance of Lombard's revolver. Lombard insists that it simply reappeared, while Blore proclaims that the revolver's reappearance doesn't make sense. Blore suggests that the only "honest" thing to do is to lock up the revolver with Armstrong's drugs, but Lombard refuses. Blore states that his refusal is proof of his guilt, and Lombard argues in defense. Claythorne interrupts the argument, reminding them of the two relevant lines of the rhyme: "Four little Indians going out to sea; A red herring swallowed one and then there were three". She insists that the lines prove that Armstrong isn't really dead; he's simply hiding. The men consider her suggestion, and when Blore points out that referring to a red herring in the poem is a bit crazy, Claythorne proclaims that Armstrong, indeed the entire situation, is crazy. Blore notes that the next line of the rhyme refers to a zoo, and there obviously isn't a zoo on the island. Yet Claythorne suggests that they, the guests, have become the zoo.
The three spend the morning on top of the island's hill, signaling the mainland with a mirror. They also undertake another unsuccessful search for Armstrong. Claythorne notes that she feels much safer outside and suggests that they remain in the open. Lombard seconds her thought, but Blore notes that they will have to find some place to spend the night and comments that they will have to return to the house. Claythorne is upset by the notion, but Lombard consoles her by noting that she will be safe in her room. Claythorne feels almost happy in the sunlight. Blore inquires about lunch, and Claythorne exclaims that she won't return to the house, adding that she will be all right in the open. Lombard offers to go to the house with Blore, but Blore tells him that he needs to remain with Claythorne. At this remark, Lombard asks Blore if he is afraid of him, noting that if he desired he could simply shoot both of them right then. Blore concedes the point, but notes that this wouldn't be according to "plan", for it wouldn't suit the nursery rhyme. Blore suggests that Lombard lend him the revolver for his trip to the house, but Lombard declines. Blore then heads for the house alone.
Claythorne asks Lombard if Blore is taking a needless chance, and Lombard replies that it isn't too risky since Armstrong doesn't have the revolver and Blore is physically stronger than Armstrong. Lombard then asserts that he knows Armstrong isn't in the house. When Claythorne asks how this could be possible, Lombard states that Blore is the murderer. Lombard comments that he isn't sure how Blore disposed of Armstrong's body, but they don't really know the truth about Blore and he certainly could have committed every murder. Claythorne wonders what will keep Blore from killing them, and Lombard states that he is prepared to protect them. When Lombard remarks that it's interesting that she trusts him, Claythorne says: "One has got to trust someone . . ." She then adds that she still believes Armstrong is the murderer. Claythorne discusses how she feels like someone is watching them and mentions having read a story involving some other-worldly visitors coming to Earth and meting out justice. Lombard remarks that their murderer is undoubtedly of this world. He then asks if Claythorne actually killed Cyril. She immediately denies the accusation, but Lombard reaffirms the accusation and suggests that there was probably a man involved. Claythorne concedes the point, and Lombard tells her that is all he needs to know. The pair hear a very loud, ground-shaking noise from the direction of the house, and Lombard suggests that they investigate. When they reach the house, they discover Blore's body, his head crushed by a large chunk of marble, which has apparently been thrown from the window above in Claythorne's room.
Lombard announces that Armstrong must be still alive, and he informs Claythorne that he will try to catch him. Claythorne suggests that this is just what the killer wants, and Lombard changes his mind. They debate how Armstrong might have hidden himself in the house. Lombard again stresses that he'd like to catch Armstrong, reminding Claythorne that he possesses the revolver. She replies that he assured her that Blore would be safe against Armstrong and yet Blore was now dead. What he forgot, she notes, is that Armstrong is mad, and a madman is more cunning than a sane man.
Lombard asks Claythorne what she proposes they do when night falls. When she has no reply, he suggests that since the weather is better they could find someplace near the cliffs. She consents and they begin hiking to higher ground. As they move along a line of rocks overlooking the sea, Lombard spots something unusual on a large rock near the water's edge. Claythorne suggests that it looks like clothing. The pair head to the water's edge, only to discover Armstrong's drowned body.
The guests' suspicion of each other nearly comes to a head. As Claythorne's comment that the remaining three have become a "zoo" suggests, they have become somewhat animalistic. Their sense of self-preservation is very strong.
The fact that the guests are only safe in their rooms implies that the only way to keep their secrets and to remain undetected is to completely isolate themselves. Of course, such isolation is impossible.
Claythorne's recollection of the story about visitors from another world illustrates her disturbed mental state and suggests that she may be breaking from reality.