what were the details of the plan?
The first meeting between the five conspirators took place on 20 May 1604, probably at the Duck and Drake Inn, just off the Strand, Thomas Wintour's usual residence when staying in London. Catesby, Thomas Wintour, and John Wright were in attendance, joined by Guy Fawkes and Thomas Percy.
Gunpowder Plot
The first meeting between the five conspirators took place on 20 May 1604, probably at the Duck and Drake Inn, just off the Strand, Thomas Wintour's usual residence when staying in London. Catesby, Thomas Wintour, and John Wright were in attendance, joined by Guy Fawkes and Thomas Percy. 
who tried to blow up what in 1605 Robert Catesby planned  to blow up the House of Lords during the State Opening of Parliament in 1605
wiki:7702540
Gunpowder Plot [SEP] Initial planning
The first meeting between the five conspirators took place on 20 May 1604, probably at the Duck and Drake Inn, just off the Strand, Thomas Wintour's usual residence when staying in London. Catesby, Thomas Wintour, and John Wright were in attendance, joined by Guy Fawkes and Thomas Percy. Alone in a private room, the five plotters swore an oath of secrecy on a prayer book. By coincidence, and ignorant of the plot, Father John Gerard (a friend of Catesby's) was celebrating Mass in another room, and the five men subsequently received the Eucharist.