Dr. Phillips, a marine biologist, enters his cramped laboratory on what is now Cannery Row in Monterey, California. White rats run about in their cages. Captive cats used in laboratory experiments meow, hungry for milk. A cage full of snakes, which seem to recognize Phillips, pull in their tongues.

Phillips lights his fire, sets a kettle of water on the stove, and drops his dinner, a can of beans, into it. He goes into his Spartan bedroom, removes his boots, and returns to the other room, where he empties a sack of starfish on the dissecting table, preparatory to beginning an experiment with them. He then takes a bottle of milk and heads for the cat pen. Before he feeds the cats, he removes one, strokes it, then puts it into a sealed box attached to a gas jet, which he turns on. As the cat inside struggles softly, he feeds the others.

As Phillips sets up his starfish experiment, he hears soft footfalls on the stairs, then a sharp knocking on his door. Opening it, he finds a tall, lean woman, straight black hair close to her head, dressed in a dark suit. Her eyes glitter in the light. Protesting that he is busy and in the middle of an experiment that must be carefully timed, Phillips tries to put her off, but she finally persuades him to admit her. Phillips explains his experiment to her and asks if she wishes to look through his microscope at part of it. She declines.

During a ten-minute lull between the timed stages of his experiment, Phillips takes the dead cat from the box in which it has been gassed and secures it on a cradle. After deftly cutting into one of its arteries, he pumps embalming fluid into it.

When Phillips finally has time to talk with the woman, she asks him whether he has a male rattlesnake. Phillips has one that he knows is male because he has seen it copulating. The woman offers him five dollars for the snake but wants him to keep the reptile in captivity for her. She then asks him to feed her snake a rat, for which she pays him. Reluctantly, Phillips puts the rattlesnake into a separate cage, then snares a live rat to drop into the snake’s cage. The woman stands and watches as the doomed rat preens. The rattlesnake advances toward it, snaps it up in its unhinged jaw, and begins to swallow the struggling animal. Finally, only a bit of the rat’s tail can be seen.

Phillips notices that as the snake approaches the rat, swaying back and forth, the woman also sways. He cannot stand to watch the snake consume the rat, nor can he look at the woman, fearing that if she is also moving her mouth, he will become sick. He returns to his experiments that, because they have been neglected for so long, are ruined and must be discarded. The woman leaves but tells Phillips that she will return and that he should feed her snake rats, for which she promises to pay him.

For several weeks, Phillips expects the woman to return, but she never does. Sometimes he thinks that he sees her in town, but on closer observation, always finds that he is wrong.