A lesson to teach/revise structures with the conditional perfect. Ideal for a small class, each member of the class becomes an investigator of one particular structure, and then in a mini-carousel, students explain their findings to each other and write notes on the summary sheet. If there is an odd number (as in my class), you can use the slot with the student to do some specific oral work or other challenging activity. Extension activity on reverse is on the future perfect. Very challenging - not for the faint-hearted!