Two people are critically ill after being struck down by nerve agent Novichok, the same substance that nearly killed former Russian spy Sergei Skripal and his daughter in March in a English town close to this latest incident.
* What's the priority now?
How this man and woman, aged in their 40s, came into contact with the deadly nerve agent is the top priority, Assistant Commissioner of Specialist Operations Neil Basu at Scotland Yard says.
One hundred counter terrorism detectives are on the job, working with Wiltshire police.
Various sites in Amesbury, where this latest incident happened, and Salisbury, where it's believed the pair visited before they fell sick, have been cordoned off. No evidence shows either of these two people visited any of the sites decontaminated following the Skripals attack.
* What are the possible links?
Investigators are "not in a position to say whether the nerve agent was from the same batch the Skripals were exposed to", Mr Basu said, but he added any possible link is clearly a line of inquiry.
Scientists will determine if the nerve agents used came from the same batch.
* We're the new victims deliberately targeted?
"That is a theory but it's speculation at the moment", Basu said, adding there is no evidence pointing to that and nothing in their background to suggest they were targeted.
* What is the UK government doing?
Home Secretary Sajid Javid is chairing a meeting of the government's Cobra emergencies committee on Thursday. Officials also met on Wednesday to be briefed on the latest. Cobra meetings address national crises and are designed to make swift and direct decisions.
* What do Public Health England say?
The Skripal case means there's a "well established response" in place to deal with the latest case, Chief Medical Office for England Professor Sally Davies said, adding anyone should visit a doctor if they have any symptoms.
"Highly precautionary" advice was issued by Public Health England to anyone who visited five locations identified by police between 10pm last Friday and 6.30pm on Saturday.
Other precautions include: washing clothes, wiping items like phones and handbags and handwashing jewellery.
* Should people be worried?
Prof Davies said risk to the general public remains low.
