The majority of pundits had penciled in the Reform Party as winners months ago, but the race has since opened up, with the Center Party surging in polls and the possibility of the Conservative People's Party or the Free Party, or both, sneaking past the the 5-percent barrier higher than ever.
Scenario one: Center wins but is left in isolation
Edgar Savisaar's Center Party wins the popular vote, and, many would say, the election. Center has somewhere between one-quarter and one-third of the seats in Parliament, as does Reform.
But Reform and Center, two parties that have been in a coalition in the past, have been at each other's throats for at least the last four years, and will not partner up, even though it is the only two-party combination that will result in a majority in Parliament.
Nor does Center have any luck with the Social Democrats, who turn in another anemic showing. The combined Center + Social Democrats would fall short of a majority in any case.
The Reform Party + Social Democrats - the current coalition - similarly finds itself short-handed this time around. But with the help of some more defections (Kadri Simson, Jüri Ratas), they cobble together an apparent majority. The president tasks Edgar Savisaar to form the government, but this is a formality. Savisaar concedes and incumbent Taavi Rõivas gets the nod.
Could it happen? It is the scenario that matches the most recent polls.
The key factor: finding the few Center Party (or Free Party) MPs who would switch sides. Party leadership has much internal opposition, including high-level MPs. The question is whether they are ready to quit immediately and at what price.
Scenario two: Left turn with a populist twist
The Social Democrats defy short-term poll results and vindicate long-range political cycle logic, picking up 30 seats, the same number as Center and more than Reform.
The so-called right populist parties such as the Conservative People's Party and Free Party also get into Parliament, too, clearly siphoning support away from the mainstream right-liberal parties like Reform and IRL.
Instead of working with either camp on the right at all, the Social Democrats go into government with the Center Party.
Could it happen? It sounds like Sweden's 2014 result, but it's dicey here. The Social Democrats have a history of underperforming at elections, and the smart money is that there are already back-room deals in place against working with Center and its "unpalatable" chairman.
The key factor: the SDE-Center partnership will be a plan B for the Social Democrats, and a strong card to play in any negotiations with the Reform Party.
Scenario three: status quo
Long before midnight, the Reform Party headquarters is a sea of celebration with cries of "four more years!" It looks like the party will pick up well over 30 seats, probably more than its 33 in the 12th Parliament. Center is second. The Social Democrats and IRL manage less than 40 seats combined.
Reform flirts with the idea of putting aside animosities and going into government with Center - after all, it worked so well in managing the ideologically different Social Democrats - but in the end opts to continue with two lapdogs, the Social Democrats and IRL. It's the same coalition as under Ansip's first term. Or alternatively, the Free Party might be brought in.
Could it happen? It's highly probable that Center will not be in the government and that the current parties will continue.
The key factor: the number of seats IRL and the Social Democrats will win, of course. The Reform Party would love a bidding war between IRL and SDE. As for Reform needing two minority partners, it might find itself overwhelmed by requests and much diplomacy will be needed from Rõivas.
Scenario four: It's all "right"
Reform hold long talks with SDE over continuing the coalition, but in the end finds the social measures too expensive and opts for IRL and the Conservative People's Party (EKRE) or the Free Party. The key question is which ministerial post EKRE or Free will get. They have the 6-7 MPs to give Reform+IRL a majority, but will want something in return, like the Interior Ministry.
Could it happen? Sure. The question is will IRL outperform its low poll data - it has in the past. And a new party would have to get into Parliament - it's been quite a long time since that last happened.
The key factor: the cost. EKRE will ask for a high-profile ministry, such as economy or defense. IRL will get defense in any case, and Reform will not want to risk a Helme as a top-level minister, and will seek to push something light, preferably environment of welfare. Will EKRE play hardball or settle for any ministry?