Sesame seed

Castor seeds are the source material for ricin in the investigation, connecting an ordinary plant and an easily obtained seed to a lethal poisoning case. Their central significance is twofold: they explain where the poison can come from, yet their widespread availability makes it difficult to identify who acquired or prepared it. The seeds become both a concrete object of forensic explanation and a problem of investigative scale.

Source and Properties

Ricin is produced from the seeds of Ricinus communis, the castor oil plant. The seeds themselves are poisonous, but the scientist explains that they are likely to prove fatal if eaten only when chewed. Six seeds are presented to Jo in a small brown envelope, making an abstract toxicology lesson tangible within the investigation. Their modest appearance contrasts with their danger: the seeds are described as similar in size and colour to pinto beans, and Jo examines one with its oval shape and two small yellow protrusions.

The scientist emphasizes how accessible the material is. A packet of ten seeds can be bought online or from nurseries for less than a pound; larger quantities, sometimes up to two kilograms, are available on the dark web. A person with a greenhouse or conservatory could also grow castor plants and maintain a supply. This range of possible sources means that no single purchase route can be treated as the necessary explanation for the poison used in the attacks.

From Seed to Investigative Clue

The seeds matter to the case because ricin derived from them is identified in a pellet recovered at Worsley. Jo tells Nick that the pellet from the seventh tee contained ricin and that Ronnie O’Neill died of ricin poisoning; she considers Morris Grimshaw’s death almost certainly connected in the same way. The evidence therefore moves from the plant’s seeds, through the poison, to a specific object associated with the attacks and the deaths under investigation.

Laboratory examination gives that connection material detail. The recovered pellet is lead with a small amount of antimony, and its head contains nine drilled holes, each three millimetres deep and half a millimetre wide. Investigators find ricin powder in some of the holes, alongside other residues; in two holes, undisturbed ricin powder lies beneath beeswax. The pellets are not castor seeds, but their contents make the seeds’ poison relevant to the physical evidence. The distinction matters: the plant identifies the toxin’s source, while the pellet provides a means by which the toxin was delivered and recovered for analysis.

Availability and the Search for a Supplier

Once the deaths are linked to ricin, the investigators consider tracing people who bought castor seeds in quantity. Nick reports that the work is progressing slowly because the seeds are not a proscribed substance and retailers do not maintain lists of purchasers. They must search credit-sale data, while anyone who paid cash may be virtually untraceable. The possible supply paths described by the scientist—ordinary retail, online purchase, dark-web acquisition, or home cultivation—help explain why a seemingly specific poison does not immediately yield a specific suspect.

Jo rejects the implication that the substance should simply be prohibited, pointing out that almonds, cherries, apples, and pears also contain cyanide in their kernels, pits, or pips. Her response frames the investigative problem without treating availability alone as proof of wrongdoing: a naturally occurring poison source is not, by itself, a reliable marker of intent. The case needs evidence that connects a person to preparation or use, rather than the mere fact that seeds can be bought or grown.

Communications and Narrative Significance

Jo proposes approaching GCHQ because it monitors communications for terms that might indicate terrorist activity and might therefore have ricin-related search activity within its reach. Nick cautions that such monitoring would be useful only if the person responsible, or someone they contacted, was already on the agency’s radar. Jo counters that searches for ricin or places to buy it online, including on the dark web, are not necessarily random signals. The exchange shows how investigators weigh a possible information source against the limits of its coverage; the existence of a keyword or a purchasing search cannot by itself guarantee that the relevant person will be found.

Castor seeds thus occupy an important point in the novel’s chain of inference. Their familiar appearance and legal availability resist the idea that an unusual toxin must have an equally obvious supply trail. At the same time, their relationship to ricin gives the investigation a route from botanical source to laboratory finding and from laboratory finding to further inquiries. The seeds are neither a complete solution nor an incidental detail: they explain the poison’s origin while exposing how much remains unknown about its acquisition and use.