The gist of the story is that scientists on a deep-space expedition unexpectedly run into (not literally) an alien ship doing the exact same thing. They work out a way of communicating with each other, but the problem is that while the aliens say they want to be friends and don't have notions of conquest in mind, blind faith that they're telling the truth risks not only the ship and the lives of the crew, but potentially the lives of the entire human race. The story primarily focuses on the human assigned as the radio operator who communicates with the aliens and his conversations with the rest of the crew.
As the human captain sees it, the primary objectives of his ship are to find out everything they can about the aliens and get that information back to Earth, subordinate only to preventing the aliens from finding out anything about the location of Earth and getting that information back to their home planet. The aliens feel the exact same way. The alien communicator at one point sends a message to the effect "You guys are nice. It's too bad we'll probably end up having to kill each other."
The story provides examples of:
- Aliens are Bastards: Maybe. We're not sure, and nobody's going home until we are sure, or the aliens are dead. Which would make humans the "alien bastards".
- An Offer You Can't Refuse: The human captain hatches a plan to make one of these to the aliens. Immediately after his ultimatum, several of the aliens collapse in convulsions; it's revealed they're laughing because the alien captain was just about to make the exact same offer.
- Bizarre Alien Senses: The alien race can transmit and receive information via radio waves, giving them what amounts to telepathy relative to us. But conversely, they have no ability to detect or transmit information via sound, giving us effective telepathy relative to them.
- Cutting the Knot: Each ship wants to get home with as much knowledge as possible about the other race, but neither knows how fast the other ship can travel, and neither can afford to have their counterpart follow them back. The ultimate solution? Switch ships. Each of them can purge their own ship of any information they don't want the other to have and destroy the weapons and the systems for tracking FTL travel. Then each of them can travel to their home, with more information about the other race than could be gotten back in any other way, knowing that their counterpart crew can't attack or follow them.
- Faster-Than-Light Travel: FTL travel is possible, but only in a perfect vacuum. At the time, many astrophysicists believed that interstellar space was completely particle-free, which later turned out not to be the case.
- First Contact: Obviously.
- Fool's Map: The humans want to discuss astronomy with the aliens, and to aid this they send the aliens some mock-ups of star maps, realizing that a real star map would give away too much information about Earth's location. When they get some maps back from the aliens, their astronomers briefly drive themselves nuts trying to figure out from what point in the galaxy star maps might look like that ... until they realize the aliens just sent back the same maps distorted slightly.
- "Hell, Yes!" Moment: The humans find out that the aliens see by infrared light, meaning that they probably evolved in a red dwarf system, giving the humans a leg up on knowing where the alien home world is.
- Higher-Tech Species: Neither race knows if the other is this or not, and neither wants to gamble on it by starting a fight and finding the other has better weapons, or by turning and running and finding out the other ship is faster or has better tracking capabilities.
- No Biochemical Barriers: The humans mention that the aliens are similar enough to humans in biochemistry that they could inhabit Earth, and conversely humans could presumably inhabit the alien home world. This is one more reason why neither race can risk trusting the other.
- Not So Different: After the ships depart, one of the humans states he believes the two species will probably end up getting along (or at least understand one another) because, while both crews were preparing their ships for departure, lower ranking crew members of both ships were telling each other dirty jokes that both groups found hilarious.
- No Warping Zone: When "First Contact" was published, many astronomers believed that outer space was a perfect vacuum. The human-piloted star ship in this story could only travel faster-than-light in a total vacuum — even the slightest wisp of atmosphere or nebula would be enough to prevent it.
- Oh, Crap!: Shortly after the humans deduce the alien star is probably a red dwarf, they realize that the same logic can be used by the aliens to determine that humans probably evolved in a yellow dwarf system. The story doesn't specifically mention it, but this is a significantly worse than even exchange, since there are a lot more red dwarfs than yellow ones.
- Prisoner's Dilemma: The paradox the two ships find themselves in. Both sides agree that the best possible outcome would be for both ships to return to their homes, allowing each to inform their species of the other's existence and preserving the possibility of peaceful exchange between the two races. Conversely, if one ship fires on the other, then at best the firing ship returns home with the knowledge of the other race's existence, but no information on their location, intent, or capabilities, and the near-guarantee of war. More likely, both ships will be destroyed or crippled, leaving both races ignorant. The problem is that, since neither race knows how fast the other ship can move through FTL or how good their sensors are, if one ship leaves the other may be able to tail it back, learning the location of the other race's homeworld.
- Properly Paranoid: The story ends before we find out for sure whether the aliens are potential allies and trading partners or bloodthirsty conquerors, but given the stakes, the initial paranoia is certainly justified.
- Take a Third Option: Both crews realize their obvious options are to run and hope the others can't (or won't) follow, fight it out and hope to win (or at least cripple the other), or just sit there until something happens to give one of them an advantage. Then they figure out an option that allows both crews to go home safely, and allows some sharing of information in hopes of peaceful relations without revealing more than either is willing to give up.
- Universal Translator