So where and what did Jesus do according to the Quaran - was he crucified? - and what is promised upon his return?
Jesus Christ in the Quran
Jesus was an apostle of God, like many other apostles that had passed away before him; he invited people to worship God alone without associate or equal, and he did not glorify himself but glorified his Lord Who had created him and sent him to the Children of Israel as an apostle.
Jesus Christ - salam be to him - was a son of man, not any son of God: God is the Eternal and has not any son or wife.
About his second coming, there is a prophetic tradition that "The son of Mary is about to come down [from heaven] to be a just arbiter among you."
These ayat are in the Quran 4: 156-159
وَقَوْلِهِمْ إِنَّا قَتَلْنَا الْمَسِيحَ عِيسَى ابْنَ مَرْيَمَ رَسُولَ اللّهِ وَمَا قَتَلُوهُ وَمَا صَلَبُوهُ وَلَـكِن شُبِّهَ لَهُمْ وَإِنَّ الَّذِينَ اخْتَلَفُواْ فِيهِ لَفِي شَكٍّ مِّنْهُ مَا لَهُم بِهِ مِنْ عِلْمٍ إِلاَّ اتِّبَاعَ الظَّنِّ وَمَا قَتَلُوهُ يَقِينًا . بَل رَّفَعَهُ اللّهُ إِلَيْهِ وَكَانَ اللّهُ عَزِيزًا حَكِيمًا . وَإِن مِّنْ أَهْلِ الْكِتَابِ إِلاَّ لَيُؤْمِنَنَّ بِهِ قَبْلَ مَوْتِهِ وَيَوْمَ الْقِيَامَةِ يَكُونُ عَلَيْهِمْ شَهِيدًا
The explanation:
(And because of: that they [: Jews, again] disbelieved [in Jesus, in addition to heir disbelief in their prophets], and [because of] that they uttered against Mary [his mother] a grave false charge [accusing her with adultery].
And [because of] their saying [in a way of boasting and mockery]: “We slew the Messiah [the Christ] Jesus, son of Mary, the apostle of God”;
But they did not slay him, nor crucified him, but a similitude1 was made for them, and those who differ therein are full of doubt thereof, with no [certain] knowledge, but only conjecture to follow; they slew him not for certain.
But God raised him up to Him; God is All-Mighty, All-Wise.
And there shall be none of the People of the Bible [Jews and Christians] but shall believe in him before his death*; and on the Day of Judgment he will be a witness against them.)
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1 They crucified Barabbas: another man like Jesus in shape: Pilate crucified Barabbas who was in jail for some crimes; so Pilate put masks on this man and crucified him and told Jews that he had crucified Jesus, while he released Jesus after telling him to hide himself from Jews and Jesus went to Syria to die later on near Damascus. And thus was Jesus saved from the plight of his enemies.
* [i.e. that he was not crucified, and that he was seen alive, three days after the event (when they crucified another man that was like him.)
Following that event by some period of time, he died at his hour of appointment, and his soul ascended to heaven, to the paradises, in the neighborhood of his Lord.]