On the face of it, tomorrow's parliamentary by-election in this north Indian district is only one of seven being held around the country. But in fact, it is the only one that Prime Minister Rajiv Gandhi's ruling Congress (I) Party cannot afford to lose.
The Allahabad vote has been turned into a referendum on Mr. Gandhi's style of government because the opposition candidate is his own former finance minister, Viswanath Pratap Singh. Mr. Singh resigned last year when his crusade to expose official corruption became too embarrassing and politically touchy for Gandhi.
Since his resignation, Mr. Singh has continued his crusade and traveled the country accusing Gandhi's coterie of aides and friends of having made big money out of defense deals.
Singh reportedly decided to contest the Allahabad by-election because the seat was earlier represented by Amitabh Bachchan, India's top movie idol and the prime minister's close friend. To Singh, the movie star is the embodiment of what has gone wrong with Gandhi's government. Mr. Bachchan resigned last year, causing the by-election to be called, when his name was dragged into foreign-exchange violations in which his brother was implicated.
Allahabad is crucial to Gandhi also because it is in India's largest state, Uttar Pradesh, which - with 85 out of 546 seats in Parliament - usually decides who becomes prime minister.
If Singh wins, it would be seen as an indication of the ruling party losing support in its last bastion of the Hindi-speaking heartland of north India. Nine out of India's 16 major states are currently run by opposition governments. And last year Gandhi suffered a major blow when his party lost the key north Indian state of Haryana to the opposition.
The importance of Allahabad has not been lost on the opposition parties who have decided - in an almost unique gesture - to jointly back Singh as their candidate. If he wins he would be seen as the man most likely to lead the opposition into battle in general elections scheduled for next year.
The Congress (I), equally aware of the importance of Allahabad, dithered until the last minute about who should be its candidate. Until the 11th hour, it looked like it would be Mr. Bachchan.
But the party finally announced its candidate would be Sunil Shastri, the noncontroversial son of former Indian prime minister Lal Bahadur Shastri, whose main asset is a clean image. Mr. Shastri himself resigned last year from the Uttar Pradesh State government on the grounds that the Congress (I) chief minister was corrupt.
This is being fully exploited by Singh, who has turned the election into a battle between corruption and integrity.
Singh, who is a scion of one of Allahabad's former royal families, has sought to portray himself as the harbinger of a new kind of politics in which big money is not considered necessary to win an election.
He has conducted his campaign mainly on foot, despite temperatures soaring into the high 90s, and has traveled from village to village (where most of the constituency's 800,000 voters live) by motorcycle. Expenditure on cars, posters, and big public meetings have been restricted to the barest minimum - to the chagrin of the various opposition parties that he represents.
The Congress (I) has itself been forced to cut down large-scale displays of money-power, and has tried to counter Singh's campaign by telling people that the opposition leaders who are backing him are not exactly above corruption themselves.
But so far Singh has a clear lead over his opponent.
Singh has said he is quite confident of victory but fears the ruling party may try to rig the election.
On Monday, Singh filed a complaint with the Election Commission saying that he had information that the Uttar Pradesh government had ``a comprehensive plan to rig the polls in favor of the Congress (I) on June 16.'' He has requested the chief election commissioner to remain in Allahabad until results are announced.
Singh's prospects in Allahabad have also improved as a result of a third candidate in the contest who claims to represent the Harijans (former ``untouchable'' caste). The Harijans have traditionally been a Congress (I) vote bank, and the possible loss of their votes could be crucial.
If Singh wins, he will have to finally decide whether he wants to be a politician or a saint.
After his resignation from government in April 1987, he swore never to hold public office again and decided to commit himself, instead, to ``cleansing'' Indian politics.
Pressure from the opposition parties has forced Singh back into electoral politics, but he still seems unsure about whether he wants to be a prime minister or a Mahatma Gandhi.