Leaders of the European Union will meet in Brussels to agree on a deal to offer Turkey what would secure Ankara's commitment to a scheme intended to halt migrant flows to the Greek islands.
A year into a crisis in which more than a million people have arrived in chaotic misery hopes have risen around the summit table that they may have found a way to at least slow the movement.
But leaders acknowledge there is no silver bullet and face many obstacles over the next two days, from howls of outrage that they plan mass expulsions of vulnerable people to a country with a patchy and worsening human rights record, to a lingering feud between Ankara and small but vocal EU member Cyprus.
"Work is progressing but there is still a lot to do," European Council president Donald Tusk wrote to leaders inviting them to the summit he will chair. After discussing the economy, the 28 EU national leaders will discuss the migration issue over dinner, starting around 8pm (0600 AEDT Friday).
A breakfast is set for Friday with Turkish Prime Minister Ahmet Davutoglu, where Tusk hopes to finalise a deal which the Turkish premier first sprang on the EU, with backing from German Chancellor Angela Merkel, at a special summit 10 days ago.
Under the deal, which was set out in fuller fashion by Tusk in a draft for EU leaders on Wednesday, in addition to a previous agreement to try and prevent the smuggling of migrants via rafts, Turkey will take back all those, including Syrian refugees, who do make it to Greek islands off Turkey's coast.
The draft, which was seen by Reuters, says the plan is "to break the business model of the smugglers and to offer migrants an alternative to putting their lives at risk". It stresses the plan is "a temporary and extraordinary measure which is necessary to end the human suffering and restore public order".
Potentially the most explosive topic, which diplomats say risks derailing the whole deal, will be how Davutoglu responds to a vague offer to open new "chapters" of Turkey's snail-like negotiations to join the EU at some distant future date.
Several of these have been blocked by Cyprus over Turkey's refusal to give it the same rights as other EU states in access to Turkish ports and airports - a result of the 42-year dispute since the violent partition of the island into a Greek-speaking state and a Turkish-speaking north recognised only by Turkey.
Cypriot President Nicos Anastasiades has made clear he will lift his veto on Turkish accession chapters only if Ankara ends its refusal to recognise Cyprus. Turkey wants concessions for its northern Cypriot allies in return. The EU and world powers are keen not to derail UN talks that could reunite the island.
Tusk's draft says the EU would work with Turkey to "prepare for a decision" on opening new accession chapters "as soon as possible" - a hazy prospect Davutoglu may not appreciate.
But in his invitation letter, Tusk stressed that only if the migrant deal could help advance the broader talks on ending the long confrontation with Cyprus, could it hope to succeed.
