240 in the shed? Coming off of the house panel I bet? You have lost a leg, so what/where is the source of the leg? A single throw double pole in the house? Maybe he used two separate ckt breakers in the house panel out to the shed and you are overlooking it? The bottom line, you lost a leg, so whats the source of your legs? If its in a shed, I assume its coming from another source, the house panel. What are your legs there out to the shed?
Good luck, be careful.