Russian opposition activist Vladimir Kara-Murza is recovering in Washington from what he claims were attempts to poison him in a politically-motivated attack in Moscow.
The Russian authorities deny any involvement in the incident earlier this year.
Mr Kara-Murza is part of the Open Russia foundation, an organisation of anti-Putin activists who call for open elections, a free press and civil rights reforms.
He told Sky News that he wants the West to take a harsher stance towards President Putin and "stand up for the principles they espouse".
But the long-time critic of the Kremlin acknowledges change needs to come from within.
Mr Kara-Murza, a US green card holder with dual British-Russian citizenship, suddenly fell ill on a trip to Moscow in February.
He had been promoting a documentary film about Boris Nemtsov, his close friend and Russian opposition leader who was shot and killed only a few hundred metres from the Kremlin in 2015.
"When the symptoms began, I knew," Mr Kara-Murza said.
"I didn't want to admit it but I knew straight away what it was because the symptoms were the same as before.
"I knew I had only a few minutes before I would become completely incapacitated.
"And I used those minutes wisely."
Mr Kara-Murza claims he was also poisoned in 2015 and said he suffered "full organ failure".
He called his wife in America, who messaged Mr Kara-Murza's main doctor in Russia.
He survived and says he now has three birthdays each year: "The one my parents gave me, and the two that the doctor has given me."
Doctors in the hospital where the 35-year-old was treated said that a "toxic substance" was to blame. He was put on dialysis.
Mr Kara-Murza can't tell you who or how, but he is convinced the Russian authorities were behind both incidents.
Kremlin spokesman Dmitry Peskov rejected his claim, saying "We never heard any, any, any, let's say, information from medics saying that he was really poisoned by some, by any substance."
But Mr Kara-Murza's situation triggered an outcry from US politicians, who have called on President Donald Trump's administration to speak on his behalf.
Senator Marco Rubio said: "Vladimir Putin does not deserve any benefit of the doubt here, given how commonplace political assassinations and poisonings have become under his regime."
The question is whether at this delicate time between Russia and the US, Mr Putin will be willing to listen.
With the spectre of Syria, old tensions are resurfacing.
The reset in relations Mr Trump hinted at could still be a long time coming.