To me, "in the available space" rules out any swapping with other rows in the grid, so we must be looking at placing THE OBJECT in the bottom row. That leaves us with interpreting "eventual." That depends on which of the accounts we are looking at. Obviously the explorer's is the last, which would require some clever word-play. I don't think any of the accounts stop with it in the vault, though that was my initial justification for putting THE OBJECT in plain text in the bottom row. Are those two letters in the bottom row meant to help us or mislead us?