Mockingbird is a S.H.I.E.L.D. agent given a cocktail of the Super Soldier serum (that turned Steve Rogers into Captain America) and the Infinity Formula (that enabled Nick Fury to survive for decades longer than a normal lifespan). The agency is understandably concerned because of the potential for interaction and side effects. So every week, she must report to S.H.I.E.L.D. for medical studies. Often different people administer these tests. Sometimes she seems to have powers. Other times, just odd symptoms, like hallucinations. (This issue mostly sets up the next four).