The escalating row over the murder of a Sikh separatist leader has the potential to derail years of close relations between Canada and India, two key strategic partners on security and trade.
The rift burst into the open on Monday when Prime Minister Justin Trudeau said Canada was investigating "credible allegations" about the potential involvement of Indian government agents in the murder of Hardeep Singh Nijjar in British Columbia in June.
India responded furiously - it "completely rejected" the allegations, calling them "absurd". Both have expelled one of the other's diplomats and it's unclear how they now pull back from the brink.
Just a few months ago, the countries were making progress towards signing a free trade agreement - long in the works - this year. Now, talks are paused and an imminent Canadian trade mission to India postponed.
So how did things reach this point?
The recent G20 summit hosted by Delhi offered some hints, key among them Mr Trudeau's tense (and short) meeting with Indian Prime Minister Narendra Modi. Then he suffered the embarrassment of having to wait in Delhi for two more days before he could leave after his plane developed a technical fault.
After the two leaders met there was no mincing of words. Mr Trudeau said Canada would always defend "freedom of expression" while acting against hatred.
In an uncharacteristically sharp statement, the Indian government said it had "strong concerns about continuing anti-India activities of extremist elements in Canada" who it accused of "promoting secessionism and inciting violence against Indian diplomats".
The reference is to calls by Sikh activists in Canada for Khalistan, or a separate homeland for Sikhs. It's a demand that evokes painful memories for millions in India, especially in northern Punjab state where Sikhs form the majority of the population (outside Punjab, Canada has the highest number of Sikhs in the world).
The demand for Khalistan peaked in India in the 1980s with an armed insurgency later crushed - thousands of people were killed. The movement is not prominent in Punjab now, and all mainstream Indian political parties vocally oppose it.
But calls for Khalistan are still loud among some in the Sikh diaspora in countries such as Canada, Australia and the UK. Delhi has reacted sharply to demonstrations for and referendums on Khalistan by Sikh activists in these countries - not illegal there, but a major irritant for India.
The issue received wider global attention after three pro-Khalistan activists died in quick succession in different countries earlier this year.
Paramjit Singh Panjwar, chief of the Khalistan Commando Force who was designated a terrorist by India, was shot dead in May in Pakistan - his killers haven't been identified yet.
In the UK, Avtar Singh Khanda, said to be the head of the Khalistan Liberation Force, died on 15 June in hospital. Khanda had been arrested in March after a demonstration in London where protesters pulled down the Indian flag at the country's embassy. But a UK police spokesperson said the death "was not deemed to be suspicious".
Three days after his death, Nijjar, also designated a terrorist by India, was shot dead outside a Sikh temple in British Columbia - it's this murder that has now led Canada to take a strong public stand against a powerful ally.
Relations between the two have survived previous strains - Canada reacted sharply to Indian nuclear tests in 1974 and 1998; India expressed its disappointment in 2005 after two Canadian Sikhs accused of a deadly Air India bombing were acquitted.
But otherwise, the two nations have mostly been on good terms, except for the Khalistan issue. They have a lot in common: "a shared tradition of democracy and pluralism" and "a common commitment to a rules-based international system", as Canada itself puts it.
They are both Commonwealth countries and members of the G20 group of leading world economies. Canada, which wants a bigger footprint in Asia, sees India as a counterweight to China.
It's not just geopolitics, the countries also have strong trade links.
India was Canada's 10th largest trading partner in 2022, with bilateral trade in goods at $11.9bn that year, up 56% from the previous year. They were very close to signing that trade agreement now on the backburner.
So there's obviously a lot at stake for both countries.
"I do think that this is a lesson to us all that there is nothing sacrosanct about India's close relationships with Western partners. This is a wake-up call that yes, India is a non-aligned player, it values its relations with the Global South, it definitely values its relations with the West. But that doesn't mean that it's going to be insulated from the possibility of a major crisis in relations," says Michael Kugelman, director of the South Asia Institute at the Wilson Center think-tank in Washington.
India's foreign minister S Jaishankar said earlier this year that Canada's response to Khalistan has been driven by "vote bank compulsion", a reference to the support Mr Trudeau's Liberal Party gets from Sikhs. Mr Trudeau's minority government is also backed by the New Democratic Party (NDP), which is led by Jagmeet Singh, himself a Sikh.
It's an assessment many Indian experts agree with.
Chintamani Mahapatra, founder of the Kalinga Institute of Indo-Pacific Studies, says that Mr Trudeau's statements on the issue of Khalistan are "divisive".
"He ignores the sentiments of the larger Indo-Canadian community, which includes the Canadian Sikhs, and appears biased in favour of the Khalistanis. Would he like external support for Quebec separatists? Of course not," he says, adding that the relationship between India and Canada has become more stressful due to Mr Trudeau.
"In the name of democracy, human rights and freedom of speech, Canada should not jeopardise its relations with other countries."
But Avinash Paliwal, who teaches politics and international studies at SOAS University of London, says the sudden escalation may not be due to just domestic compulsions.
"If your intelligence agencies have gathered credible information that another country, even if it is an ally, was involved in a covert operation on your soil, you're bound to act on that," he says, adding that it's likely that Mr Trudeau tried to raise the issue through other channels first.
According to India's statement, Mr Trudeau did bring up the allegation with Mr Modi but received short shrift.
The Canadian PM has received support from other domestic politicians, including main opposition leader Pierre Poilievre. The West has reacted too - the US says it is "deeply concerned" by the allegations, while the UK says it is "in close touch" with Canada on the issue.
Experts say that while Western countries see India as necessary to counter China's influence, there is also growing concern about the direction of Indian politics under Mr Modi - critics say attacks on minorities have risen since his government came to power, and raise other human rights concerns.
The developments will also be closely watched by Beijing and Moscow, which will be glad to see a "fissure between India and the West", Mr Paliwal says. However, he adds that this wouldn't "derail the strategic story" or "make Washington turn its back" on India.
Mr Kugelman says China and Russia will see the confrontation differently.
"Beijing does not want to see India broaden and deepen relations with like-minded countries keen to push back against China. So in that regard, this may be seen as a strategic benefit for Beijing. Russia may be perfectly happy to see Canada bogged down in this crisis," he says.
In the short term, though, an India-Canada confrontation will have geopolitical consequences. If Canada continues to issue strong statements and goes on to directly accuse India, it will present a unique challenge to Western governments, specially the UK and Australia.
The way the West backed Delhi at the recent G20 summit was a clear indication that it wants India to be a viable counterweight to China.
But it will be a strategic headache for them if it comes to a point where they have to choose between India and Canada. So far, the UK, the US and Australia have given calculated statements.
But can India and Canada still mend their differences to avoid a geopolitical challenge for the West?
Mr Mahapatra says that while the Khalistan issue can affect economic co-operation in the short term, it's unlikely to derail long-term ties between the countries. He also cautions against "extreme steps", especially from Canada.
"Expelling a diplomat means you don't want a dialogue. Such issues need to be dealt through dialogue and diplomacy, not confrontation," he says.