Plots: replace curve

How does one replace a curve with another one in a plot?
I have this loop

p = ptrans[1]
    pl = plot(vec(distances), vec(p), leg = false, ylims = (-1000, 1000))
    for i in eachindex(d["times"])
        p = ptrans[i]
        pl = plot!(pl, vec(distances), vec(p))

But it simply adds additional curves to the plot instead of replacing the one that is there. I want a single curve which changes as I go through the loop.
I use Plots with gr().

call plot instead of plot!?