Alan Pardew finds himself confronted with the most unlikely of choices. They are the product of a transfer twist few anticipated: Pardew reportedly started last week looking to bolster his midfield with Damien Johnson and eventually acquired Mascherano. It is the equivalent of looking for a hatchback to run around town in and coming home in a Rolls-Royce.
Except that Pardew has not paid for it.
To astonishment and awe, then, was added intrigue, heightened when talk of a takeover involving Kia Joorabchian, the public face of the MSI group who own the two Argentines, materialised.
That the two developments are connected is beyond dispute, but much else is open to debate. In an era of rich - and sometimes faceless - investors in football clubs and financial empires that straddle borders, impenetrable inner circles make transparency impossible.
Money headed for the Hammers may have come from Brazil, Iran, Israel, Georgia, Russia and the British Virgin Islands. Or it may not. It represents a far cry from the days when a high-street butcher was chairman of a title-winning team (Bob Lord at Burnley).
So it is easier to assess the football than the finances. Tevez, a squat, headstrong dribbler whose emergence from the slums of Buenos Aires invites comparisons with Diego Maradona, is a force of nature, seemingly incapable of having a quiet game. In contrast, Mascherano has a much more understated style, a quietly influential anchor midfielder with a maturity and a positional discipline that belie his inexperience.
Pardew's stable of strikers provide variety and speed, but none are in the same orbit as Tevez. Mullins, the club's reigning player of the year, comes from the mould of unsung heroes, but he is no Mascherano. In one sense, their selection - apparently guaranteed, if fit, as part of the terms of the transfer - is an imposition on their new manager. In another, it is a formality.
But there has been a meritocratic feel to Pardew's team of young Brits; whether that will be disrupted or the displaced will become the departed remains to be seen.
Perhaps the dropped will simply wait for the two Argentines to move on; while much is shrouded in mystery, it is hard to envisage Tevez and Mascherano deciding a love of jellied eels equates to cause to ignore the future advances of Chelsea, Barcelona, Real Madrid or AC Milan.
And wherever their eventual destination, they represent the two most exciting acquisitions of the summer. Because, while Michael Ballack and Andriy Shevchenko represent proven class, the Argentines are comparatively unknown quantities; Upton Park could witness the advent of global icons.
The last influx of Argentine excellence was equally notable for the sense of surprise, but also for the longevity and lasting impact of the arrivals.
Ossie Ardiles and Ricardo Villa joined Tottenham in 1978, and the former provided a decade's service. Few anticipate seeing Tevez and Mascherano in West Ham's class of 2016.
But why West Ham? Suggestions that both will fulfil a lifetime's ambition by lining up alongside Christian Dailly are sadly facetious. Only the vociferous contingent of former Hammers in the media regarded it as entirely right and proper that two of the most admired footballers on the planet should opt to go to Upton Park.
Undoubtedly, the Premiership presents a shop window that Brazilian football cannot offer. The World Cup provided confirmation that Tevez and Mascherano's talents would be required in Europe before long. Their choice, if a choice it is, of West Ham has prompted others, seemingly the likelier destinations for the Argentines, to explain their reluctance to sign them.
It is a question of whether MSI's machinations backfired, whether clubs were deterred by the asking price or if, after being outflanked by West Ham, they are merely attempting to save face.
MSI's original intentions have been compromised by Joorabchian's takeover plans. As a business model, the concept of bypassing feeder clubs and owning players who would earn global repute and commensurately high transfer fees was, providing such footballers were successfully identified, perfect in its simplicity.
It guaranteed profit without the costs and pitfalls of owning clubs. The sporting connotations are more worrying for all those who believe the club's historic role in developing talent should be rewarded with the transfer fee and the manager deserves autonomy over team selection.
The Bosman rule has had a corrosive impact on some clubs, but proceeds MSI generate is money lost to football.
Moreover, while the unquestioned excellence of the two Argentines can only aid West Ham, a similar policy of imports could undermine Pardew's authority, although the stringent rules on work permits in the UK, as Liverpool can testify after their lengthy pursuit of Mark Gonzalez, makes it easier to recruit South Americans in Spain or Portugal.
Signing Tevez and Mascherano, under their current ownership, is, in one sense, a no-lose deal. Football clubs' understanding of credit proved somewhat faulty a few years back, buying players on the never-never that plunged them into debt and, in some cases, bankruptcy.
The Argentinians are on hire, not the costlier hire-purchase, and have the quality to catapult West Ham into contention for a Champions League place. Even if that leaves Pardew to fund their successors, their impact would be beneficial.
It would also, lest we forget, be entertaining. From a footballing perspective, Tevez and Mascherano are a boon to the Premiership as well as West Ham. Whether the same can be said for Joorabchian is unclear.
In a world of seemingly murky deals there is an irony that the name of Tevez and Mascherano's former club, Corinthians, evokes the amateur ideals of Victorian England.
The undisclosed fee is a blight on the modern game where the culture of secrecy can be damaging; the undisclosed owner, with unaccounted-for finances, can be still more dangerous. Excitement on the pitch should be accompanied by transparency off it.