no win no fee agreement

Hi,
Recently I've been involved in a card accident as a passenger and i went to seek an advice to solicitor. He sent me so called "no win no fee" agreement, which seems very tricky. In our conversation he said that in any case/if i win or lose/ I should not pay him anything, he'll ask the opponent, but in the agreement is written i should pay the solicitor basic charges, disbursements and 50% of basic charges succesful fee if I win.
Shall I sign it? help, pls