Agnew disappears on Mars after entering a passage between two rocks, and the surviving accounts leave open whether he was killed, lost, or vanished outright. The incident changes Captain van Tromp’s view of the Martians: despite their outwardly peaceful behavior, they no longer seem merely harmless, and years later he still wakes wondering what became of his missing medical officer.

The disappearance

Lieutenant Agnew was the expedition’s junior medical officer, a brilliant specialist whom Captain van Tromp had otherwise found unproblematic and well liked. His concealed prejudice, however, was directed against Martians. After the crew judged the Martians peaceful, van Tromp ordered the men not to carry weapons outside the ship, fearing that an armed encounter could provoke an incident. The later discovery that Agnew’s personal sidearm was missing, together with the testimony that he wore it, suggested that he had disobeyed that order.

Two crewmen saw Agnew enter a passage between two large rocks, an unusual kind of formation on the otherwise monotonous Martian terrain. A Martian went into the same passage after him. Knowing Agnew’s hostility, the crewmen hurried to intervene. Both heard a shot, but their observations afterward did not agree in every detail: one arrived soon enough to glimpse Agnew beyond the Martian, which nearly filled the narrow opening, and then saw him disappear; the other reached the passage as the Martian was coming out.

Once the Martian had passed, both men could see that the passage ended in an empty dead end. The testimony offered no visible route by which Agnew could have escaped. Van Tromp later considered whether he might have jumped over the rock wall, helped by Mars’s low surface gravity and the force of fear. But van Tromp had tried the jump himself and could not make it, leaving that ordinary explanation uncertain rather than conclusive.

The official explanation

The witnesses wore breathing equipment, which they had to use on Mars. Van Tromp pointed out that hypoxia could make a person’s senses unreliable and entertained the possibility that the man who reported seeing Agnew vanish had been affected by oxygen deprivation. He ordered the crewman to check his demand valve and the rest of his breather equipment before going outside again. This offered a practical explanation for the strangest testimony, but did not establish what had happened in the passage.

At first, van Tromp expected Agnew to return. He planned to reprimand him for carrying a weapon, if he had done so, and for going out alone, which seemed clear. Agnew never came back. The crew searched for him, but found neither him nor a body. Van Tromp publicly treated the mystery as an ordinary disappearance: Agnew had become lost among the rocks, died after running out of oxygen, and perhaps been covered by drifting sand. Winds at sunrise and sundown could move the sand, making that final possibility credible without providing proof.

The captain did not tell the witness to keep quiet. Instead, he made clear that the story was hard to believe, especially because the other crewman could not corroborate the account of an instantaneous disappearance. The official version prevailed. Van Tromp had also downplayed the incident because he could not risk panic among people a hundred million miles from home. He used Agnew’s loss as a warning to enforce tighter precautions: travel in company, remain in radio contact with the ship, and check breathing equipment.

Van Tromp’s changed view

Before Agnew vanished, the Martians had seemed to van Tromp large, gentle, harmless, and even rather comical. The expedition had experienced no trouble with them; once Sven Nelson worked out how to ask, they gave the crew whatever it wanted. But the unexplained shot, the Martian’s presence in the passage, and the empty dead end unsettled that easy impression. Van Tromp dates his own misgivings about the Martians to this incident, even though he could not identify them as the cause of Agnew’s disappearance.

The captain’s account preserves that uncertainty rather than resolving it. Agnew may have died through familiar hazards—an armed excursion, isolation, failing oxygen, or shifting sand—or the witness may have seen something beyond those explanations. The available evidence establishes neither a Martian attack nor a supernatural disappearance. It establishes that the missing weapon, the shot, the conflicting observations, and the fruitless search left the case open.

The story’s later disclosure

Van Tromp eventually recounts the incident in a private conversation among water brothers. Mahmoud says that he had previously heard only the official account and prefers it to a mysterious explanation; he is not inclined to superstition. The disclosure therefore does not overturn the expedition’s public version. It reveals instead how effectively that version concealed the captain’s own doubts: only van Tromp and Sven had heard the witness’s extraordinary report, and they kept it to themselves.

The memory has not settled with time. As he finishes the story, van Tromp suddenly looks old and admits that he still wakes in the night asking himself what became of Agnew. The disappearance remains both a disciplinary warning and an unresolved loss: an episode the captain converted into practical rules for the crew, while privately carrying the question those rules could not answer.