Gumnaam ("unnamed, anonymous") is a slapdash, inadequately scripted, totally non-suspenseful mystery. It is nevertheless great fun to watch, thanks entirely to a passel of thoroughly entertaining songs and fun comic performances by the likes of Helen and Mehmood.
A group of strangers at a masquerade party are delighted when they are chosen, apparently at random, as winners of an exciting foreign vacation. The trip gets off to a rough start, however, when an emergency forces their plane to land in a remote wilderness. And things take an even more sinister turn when the plane takes off, leaving them stranded. Soon they find an isolated mansion, tended by a valet (Mehmood) who knows their names and seems to have been expecting them. A mysterious diary in the mansion reveals the reason they are there: It says they are each responsible for an unjust death, and will be forced to pay the ultimate price. And sure enough, one by one the travelers begin to die violently ... and the murderer must be among them.
Gumnaam takes Agatha Chrtistie's Ten Little Indians as its inspiration. It follows that classic story fairly faithfully, but Gumnaam is very light on the plot details that made the original tight and compelling. There is no real payoff - the killer's motivation for assembling this particular group is stated, but with a few exceptions we are told neither whose deaths they caused, nor why the killer thinks justice is his responsibility.
One result of the slapdash plotting is an utter lack of suspense, which is compounded by the travelers for the most part not behaving as if they fear for their lives. The other filmi touches, like Mehmood's broad South Indian caricature and other roles (like Pran's and Madan Puri's) played for laughs, don't bolster the story. But unlike Raat aur din, where filmi touches detract from what could have been a taut psychological drama, in Gumnaam they are the saving grace of what would otherwise be a dreadful film.
The best thing about Gumnaam is the film's songs, most of which are upbeat, splendid fun. Helen, as one of the doomed guests, gets three of these, including Mehmood's fantastic dream sequence, an adorable beachside romp, and the rare treat of a drunken buddy-song in which the revelers are both women (Helen and Nanda). And no discussion of the songs of Gumnaam is complete without mention of the wild, mod goodness of "Jaan pehechaan ho".
Gumnaam is a masala film, and so of course a romance thread is woven through as well. This thread is wasted, though, on the film's milquetoast hero and heroine, Manoj Kumar and Nanda. Greta (of Memsaab Story; thanks to her for the screencap) commented that Gumnaam would have been a totally different movie if Shammi Kapoor had been the hero, and I have to agree. It could possibly have been an all-time classic on the level of Teesri Manzil or Kashmir ki kali - with Shammi as the hero and Asha Parekh, Sharmila Tagore, or really anyone else as the heroine. Nanda and Manoj's songs are entertaining enough, but they pale in comparison to the other songs in the film; Manoj attempts Shammi-like moves, but even though he's younger and slightly less chubby, he lacks the energy and charisma that Shammi brought to his best movies.
In the end, though, even to critique a movie like Gumnaam is to ask too much of it. It is thoroughly amusing while it's happening - at its best moments, it shines - and that's all it sets out to do.