8 down: the correct answer is AISLE. The compiler has given the wrong clue. He originally wrote, for 8 down: Empty seat left by son (5). Answer: ADDLE. This meant that the answer to 11across was ELAPSED. He then had second thoughts, so he changed the answer to AISLE. The clue should for that have been: A key to the passage (5), but the compiler changed only the answer in the grid, giviing AISLE, but the clue remained as: Empty seat left by son, and nobody noticed the mistake. Saga will publish an apology in the August issue.
So, the correct answer is AISLE, but the clue does not fit because it is wrong.