Former Russian double agent Sergei Skripal, 66, and his daughter Yulia, 33, are found unconscious on a park bench in Salisbury.
Days later police say a nerve agent was used to poison the pair, and the case is being treated as attempted murder.
British Prime Minister Theresa May tells the House of Commons that the nerve agent is of Russian origin and the government has concluded it is "highly likely" that Russia is responsible for the poisoning.
Mrs May announces that the UK will expel 23 Russian diplomats in the wake of the incident, calling it an "unlawful use of force by the Russian state against the UK".
Mrs May is joined by the leaders of the United States, Germany and France in issuing a joint statement blaming Russia for the attack.
Russia retaliates by announcing the expulsion of 23 British diplomats. Russia also announces the closures of the British Council and the British Consulate in St Petersburg.
A Wiltshire Police officer, Detective Sergeant Nick Bailey, is discharged from hospital after the incident.
He releases a statement saying: "Normal life for me will probably never be the same."
Ireland is one of 22 countries that expel Russian agents, in what Mrs May calls the "largest collective expulsion of Russian intelligence officers in history".
One Russian diplomat based in Dublin is expelled.
Scotland Yard reveals that the Skripals first came into contact with the nerve agent at Sergei Skripal's home.
Yulia Skripal is discharged from hospital.
Sergei Skripal is discharged from Salisbury District Hospital, after more than two months of treatment.
Two people - Dawn Sturgess and Charlie Rowley - become ill at a property in Muggleton Road, Amesbury, 12km from Salisbury, and are taken to Salisbury District Hospital.
Initially, police believe the pair may have taken contaminated drugs.
A "major incident" is declared after police revealed that Ms Sturgess and Mr Rowley have been exposed to an "unknown substance", later confirmed to be Novichok.
New Home Secretary Sajid Javid accuses the Russian state of using Britain as a "dumping ground for poison", and demands an explanation from the Kremlin for the two episodes.
Forensic investigators in hazardous material suits and gas masks begin searching the building where Ms Sturgess lived.
Dawn Sturgess dies in hospital following her exposure to Novichok. A murder investigation is launched by Scotland Yard.
.Charlie Rowley regains consciousness the next day.
Police reveal the source of the Novichok that poisoned Ms Sturgess and her partner was a small bottle found in Mr Rowley's home.
Specialist police begin searching Queen Elizabeth Gardens in Salisbury, a park at the centre of the poisoning probe.
Police are believed to have identified the perpetrators of the Skripal attack.
Mr Rowley is discharged from hospital. He subsequently says he feels lucky to be alive, and says he believes he and his partner were poisoned after he found a "cosmetic bottle" and sprayed the "oily substance" on Ms Sturgess's wrist.
Russia angrily denounces the imposition of "draconian" new US sanctions after the Trump administration concluded Moscow was responsible for the Salisbury attack.
Independent investigator, the Organisation for the Prohibition of Chemical Weapons, confirms the toxic chemical that killed Ms Sturgess was the same nerve agent as that which poisoned the Skripals.
Scotland Yard and the Crown Prosecution Service announce there is sufficient evidence to charge two Russian nationals - Alexander Petrov and Ruslan Boshirov - with offences including conspiracy to murder over the Salisbury nerve agent attack.