During the end step before your turn, activate Isochron Scepter by paying 2 and tapping it, casting a copy of Brainstorm without paying its mana cost.
Resolve Brainstorm, causing you to draw three cards and put Temporal Manipulation and another card on top of your library, ensuring Temporal Manipulation is the topmost card.
Move to your turn, drawing and revealing Temporal Manipulation during your draw step.
God-Eternal Kefnet's first ability triggers, causing you to pay 1 to cast a copy of Temporal Manipulation.
Resolve the copy of Temporal Manipulation, causing you to take an extra turn after this one.
Activate Isochron Scepter by paying 2 and tapping it, casting a copy of Brainstorm without paying its mana cost.