Lecturing on a law course at a local college, the Chief finds that one of the students is planning to prove that the perfect crime can be committed. The person responsible appears to be particularly cold and calculating, and the Chief finds that he is facing true genius.

A Torah is stolen from a local Synagogue, presided over by an old friend of the Chief's. Ironside personally takes on the case, determined to find out if the theft was an act of vandalism, as the evidence would seem to point out, or if it is really the work of thieves looking for some quick money.

A string of murders is committed, and in each case the victim has a numbered disk in their possession. After number four is found dead, it transpires that the Commissioner is the owner of disk number six; and the Chief disguises himself as number five - an irascible artist to whom he bears a striking resemblance - in order to keep him alive.