meaning: involve somebody in
keywords
let - a plate on a house saying 'to let'
in - tin
for - four
example sentence: While you were away, I was let in for a lot of extra expense connected with the upkeep of the house.

While one friend was away, the other, sharing the house with the plate 'to let' was involved in a lot of extra expense, as the plumber, the cleaner and the decorator wanted their money. He divided the money into four piles and put each of them on big tins outside the house.