Strong on lush cinematography, period knitwear and sincerity, but less effective in terms of historical plausibility, the mostly second world war-set drama Summerland is a mixed bag – a blend of fizzy sherbet lemons and humbug. Gemma Arterton stars as Alice, a cantankerous bluestocking scholar of myths and legends who lives alone – a suspicious tendency in the eyes of the locals, especially the pesky kids who like to play pranks on her – in an impossibly picturesque cottage on the Kent coast.

Since the blitz is raging across the country, Alice has been compelled to billet an adolescent London boy named Frank (Lucas Bond, excellent and perhaps a future star), much against her wishes. But since he can’t be rehomed for at least a week, she takes him in, treats him quite rudely, but of course soon grows fond of the tousle-haired tyke who so reminds her of her lost secret love, Vera (Gugu Mbatha-Raw, luminous as usual), a vibrant young woman with whom Alice had a passionate affair back in the 1920s.

Writer-director Jessica Swale worked with Mbatha-Raw on the charming stage production of Nell Gwynn at the Globe a few years ago, so you’d think she’d have found a way to give her more screentime aside from a few gauzy flashbacks. That said, the two women have little chemistry, and the safer, less horse-frightening surrogate maternal bond between Frank and Alice is clearly where the film’s interest lies. Elsewhere, the narrative trajectory is far too predictable, and the portrait of rural England in wartime, on that coast in particular, is overly bucolic and prettified. Kent would have been crawling with military camps and coastal defences, for starters. But for every quibble there’s a counterweight pleasure, such as Tom Courtenay as a kindly schoolmaster or Penelope Wilton, as an older incarnation of Alice, hissing at local kids to bugger off.

• Summerland is in cinemas from 31 July.