Answer: Hollyhocks are susceptible to a number of leaf diseases, but based on your description I suspect the immediate problem is overwatering. Short of transplanting the plant to higher ground, which is nearly impossible with a mature hollyhock, the best you can do is hope for a spell of dry weather and hope the plant recovers.
Hollyhocks are usually very short lived and are generally classified as biennials, so it is also possible that the plant was somewhat weakened by age and the fact that it bloomed so well last year. By starting new plants each year, you'll have flowers every season.
Q&A Library Searching Tips