What is killing my plants? A 'dead' strip with growth around! Please help.

[herewegoloopyloo]

Am new to this gardening lark so no idea what this could be. Have a steep bank of fairly clay/red soil which planted (1-2 yrs ago) with ground cover (vinca etc) and perennial type flowers, incl a border of lavender and catmint. It all grew really well and was pretty established this spring, esp the catmint and lavender. Now there is a strip running along side the path where all the plants have died. The catmint has gone white/grey and died. It also looks like it may have been flattened by something - we do have a visiting cat (own fault for planting catmint) but surely that wouldn't kill it? The plants right next to this area (including adjacent vinca, lavender, catmint etc) are all growing fine.

Any ideas?! Advice gratefully received.

Soil is often drier right at the edge of a bed of soil, so it could possibly be that these plants have suffered drought more than their neighbours?

Only other poss that springs to mind is that weedkiller used on path might have blown there, or some lawn fertiliser might have been spilt there at too high a concentration for the plants to cope?

Thanks Threadworm. There is a really sharp demarcation with the dead catmint right next to catmint that is thriving so I think not drought, although that did cross my mind. Haven't used weedkiller on path (is bark on wood steps). Re. fertiliser - only thing can think of is my MIL did put some Fish,Bone and Blood (?!) fertiliser around though not sure if was there. It is where she could reach 'though and would not have been able to get further in (is very steep bank. Could it be that? THought was supposed to encourage growth!
Do badgers affect this kind of thing? I ask as we clearly have one that visits and further down the garden there is strip of dead grass which I am told is due badgers' wee! (or I am being gullible?)

Bump for the evening crowd!