Nothing happens in this issue, so spoiler alerts are useless, but...
Thousands of years ago Durlans (shapeshifting green tentacled aliens) fought unknown Kryptonians in a starship battle. An abandoned Kryptonian ship is found by S/B and one of the escape pods has been used to get to Earth (we find out later by just ONE Durlan, so not much of a threat).
THAT'S IT. Nothing else. You don't need this issue to understand the Aftermath arc. SKIPPABLE.